116824015 java-j2 ee

JAVA & J2EE
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JAVA
 Abstraction: Showing the essential and hiding the non-Essential is known as Abstraction.
 Encapsulation: The Wrapping up of data and functions into a single unit is known as
Encapsulation.
Encapsulation is the term given to the process of hiding the implementation details of
the object. Once an object is encapsulated, its implementation details are not immediately
accessible any more. Instead they are packaged and are only indirectly accessed via the
interface of the object.
 Inheritance: is the Process by which the Objects of one class acquires the properties of
Objects another Class.
A reference variable of a Super Class can be assign to any Sub class derived from the
Super class.
Inheritance is the method of creating the new class based on already existing class ,
the new class derived is called Sub class which has all the features of existing class and its
own, i.e sub class.
Adv: Reusability of code , accessibility of variables and methods of the Base class by the
Derived class.
 Polymorphism: The ability to take more that one form, it supports Method Overloading &
Method Overriding.
 Method overloading: When a method in a class having the same method name with
different arguments (diff Parameters or Signatures) is said to be Method Overloading. This
is Compile time Polymorphism.
o Using one identifier to refer to multiple items in the same scope.
 Method Overriding: When a method in a Class having same method name with same
arguments is said to be Method overriding. This is Run time Polymorphism.
o Providing a different implementation of a method in a subclass of the class that originally
defined the method.
1. In Over loading there is a relationship between the methods available in the same class
,where as in Over riding there is relationship between the Super class method and Sub
class method.
2. Overloading does not block the Inheritance from the Super class , Where as in
Overriding blocks Inheritance from the Super Class.
3. In Overloading separate methods share the same name, where as in Overriding Sub
class method replaces the Super Class.
4. Overloading must have different method Signatures , Where as Overriding methods
must have same Signatures.
Dynamic dispatch: is a mechanism by which a call to Overridden function is resolved at
runtime rather than at Compile time , and this is how Java implements Run time
Polymorphism.
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JAVA & J2EE
 Dynamic Binding: Means the code associated with the given procedure call is not known
until the time of call the call at run time. (it is associated with Inheritance &
Polymorphism).
• Bite code: Is a optimized set of instructions designed to be executed by Java-run time
system, which is called the Java Virtual machine (JVM), i.e. in its standard form, the JVM
is an Interpreter for byte code.
JIT- is a compiler for Byte code, The JIT-Complier is part of the JVM, it complies byte code
into executable code in real time, piece-by-piece on demand basis.
Final classes : String, Integer
Abstract class : Generic servlet
o variable:An item of data named by an identifier.Each variable has a type,such as int or
Object,andascope
o class variable :A data item associated with a particular class as a whole--not with
particular instances of the class. Class variables are defined in class definitions. Also
called a static field. See also instance variable.
o instance variable :Any item of data that is associated with a particular object. Each
instance of a class has its own copy of the instance variables defined in the class. Also
called a field. See also class variable.
o local variable :A data item known within a block, but inaccessible to code outside the
block. For example, any variable defined within a method is a local variable and can't be
used outside the method.
o class method :A method that is invoked without reference to a particular object. Class
methods affect the class as a whole, not a particular instance of the class. Also called a
static method. See also instance method.
o instance method :Any method that is invoked with respect to an instance of a class.
Also called simply a method. See also class method.
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JAVA & J2EE
 Interface: Interfaces can be used to implement the Inheritance relationship between the
non-related classes that do not belongs to the same hierarchy, i.e. any Class and any
where in hierarchy. Using Interface, you can specify what a class must do but not how it
does.
 A class can implement more than one Interface.
 An Interface can extend one or more interfaces, by using the keyword extends.
 All the data members in the interface are public, static and Final by default.
 An Interface method can have only Public, default and Abstract modifiers.
 An Interface is loaded in memory only when it is needed for the first time.
 A Class, which implements an Interface, needs to provide the implementation of all the
methods in that Interface.
 If the Implementation for all the methods declared in the Interface are not provided , the
class itself has to declare abstract, other wise the Class will not compile.
 If a class Implements two interface and both the Intfs have identical method declaration, it
is totally valid.
 If a class implements tow interfaces both have identical method name and argument list,
but different return types, the code will not compile.
 An Interface can’t be instantiated. Intf Are designed to support dynamic method resolution
at run time.
 An interface can not be native, static, synchronize, final, protected or private.
 The Interface fields can’t be Private or Protected.
 A Transient variables and Volatile variables can not be members of Interface.
 The extends keyword should not used after the Implements keyword, the Extends must
always come before the Implements keyword.
 A top level Interface can not be declared as static or final.
 If an Interface species an exception list for a method, then the class implementing the
interface need not declare the method with the exception list.
 If an Interface can’t specify an exception list for a method, the class can’t throw an
exception.
 If an Interface does not specify the exception list for a method, he class can not throw any
exception list.
The general form of Interface is
Access interface name {
return-type method-name1(parameter-list);
type final-varname1=value;
}
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 Abstract Class: Abstract classes can be used to implement the inheritance relationship
between the classes that belongs same hierarchy.
 Classes and methods can be declared as abstract.
 Abstract class can extend only one Class.
 If a Class is declared as abstract , no instance of that class can be created.
 If a method is declared as abstract, the sub class gives the implementation of that class.
 Even if a single method is declared as abstract in a Class , the class itself can be declared
as abstract.
 Abstract class have at least one abstract method and others may be concrete.
 In abstract Class the keyword abstract must be used for method.
 Abstract classes have sub classes.
 Combination of modifiers Final and Abstract is illegal in java.
 Abstract Class means - Which has more than one abstract method which doesn’t have
method body but at least one of its methods need to be redefined in derived Class.
The general form of abstract class is : abstract type name (parameter list);
 Diff Bet Interfaces And Abstract class ?
o All the methods declared in the Interface are Abstract, where as abstract class must have
atleast one abstract method and others may be concrete.
o In abstract class keyword abstract must be used for method, where as in Interface we
need not use the keyword for methods.
o Abstract class must have Sub class, where as Interface can’t have sub classes.
o An abstract class can extend only one class, where as an Interface can extend more than
one.
Accesss specifiers Access modifiers
Public Public
Protected Abstract
Private Final
Static
Volatile Constant
Synchronized
Transient
Native
• Public : The Variables and methods can be access any where and any package.
• Protected : The Variables and methods can be access same Class, same Package & sub
class.
• Private : The variable and methods can be access in same class only.
Same class - Public, Protected, and Private
Same-package & subclass - Public, Protected
Same Package & non-sub classes - Public, Protected
Different package & Sub classes - Public, Protected
Different package & non- sub classes - Public
 Static : access modifier signature - Variable-Static int b; Method- static void
meth(int x)
 When a member is declared as Static, it can be accessed before any objects of its class are
created and without reference to any object. Eg : main(),it must call before any object exit.
 Static can be applied to Inner classes, Variables and Methods.
 Local variables can’t be declared as static.
 A static method can access only static Variables. and they can’t refer to this or super in
any way.
 Static methods can’t be abstract.
 A static method may be called without creating any instance of the class.
 Only one instance of static variable will exit any amount of class instances.
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JAVA & J2EE
 Final : access modifier
 All the Variables, methods and classes can be declared as Final.
 Classes declared as final class can’t be sub classed.
 Method ‘s declared as final can’t be over ridden.
 If a Variable is declared as final, the value contained in the Variable can’t be changed.
 Static final variable must be assigned in to a value in static initialized block.
 Transient : access modifier
 Transient can be applied only to class level variables.
 Local variables can’t be declared as transient.
 During serialization, Object’s transient variables are not serialized.
 Transient variables may not be final or static. But the complies allows the declaration and
no compile time error is generated.
 Volatile: access modifier
 Volatile applies to only variables.
 Volatile can applied to static variables.
 Volatile can not be applied to final variables.
 Transient and volatile can not come together.
 Volatile is used in multi-processor environments.
 Native : access modifier
 Native applies to only to methods.
 Native can be applied to static methods also.
 Native methods can not be abstract.
 Native methods can throw exceptions.
 Native method is like an abstract method. The implementation of the abstract class and
native method exist some where else, other than the class in which the method is
declared.
 Synchronized : access modifier
 Synchronized keyword can be applied to methods or parts of the methods only.
 Synchronize keyword is used to control the access to critical code in multi-threaded
programming.
Declaration of access specifier and access modifiers :
Class - Public, Abstract, Final
Inner Class - Public, Protected, Private, Final, Static,
Anonymous - Public, Protected, Private, Static
Variable - Public, Protected, Private, Final, Static, Transient, Volatile, Native
Method - Public, Protected, Private, Final, Abstract, Static, Native, Synchronized
Constructor - Public, Protected, Private
Free-floating code block - Static, Synchronized
 Finalize( ) method:
 All the objects have Finalize() method, this method is inherited from the Object class.
 Finalize() is used to release the system resources other than memory(such as file
handles& network connec’s.
 Finalize( ) is used just before an object is destroyed and can be called prior to
garbage collection.
 Finalize() is called only once for an Object. If any exception is thrown in the finalize()
the object is still eligible for garbage collection.
 Finalize() can be called explicitly. And can be overloaded, but only original method
will be called by Ga-collect.
 The signature finalize( ) : protected void finalize() throws Throwable { }
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 Constructor( ) :
 A constructor method is special kind of method that determines how an object is
initialized when created.
 Constructor has the same name as class name.
 Constructor does not have return type.
 Constructor cannot be over ridden and can be over loaded.
 Default constructor is automatically generated by compiler if class does not have once.
 If explicit constructor is there in the class the default constructor is not generated.
 If a sub class has a default constructor and super class has explicit constructor the code
will not compile.
Exception handling:
 Exception class: is used for the exceptional conditions that are trapped by the program.
An exception is an abnormal condition or error that occur during the execution of the program.
 Error: the error class defines the conditions that do not occur under normal conditions.
Eg: Run out of memory, Stack overflow error.
Java.lang.Object
+….Java.Lang.Throwable Throwable
+…. Java.Lang.Error
| +…. A whole bunch of errors
| Exception Error
+….Java.Lang.Exception (Unchecked, Checked)
+….Java.Lang.RuntimeException
| +…. Various Unchecked Exception
|
+…. Various checked Exceptions.
Two types of exceptions:
1. Checked Exceptions : catched at the compile time.
Must be declare in the method declaration or caught in a catch block.
2. Un-checked Exceptions: unchecked exception is checked at run time.
Run-time Exceptions and Error, does’t have to be declare.(but can be caught).
Arithmetic,Nullpointer,ArrayIndexOutofBounds,ArrayStore,FilenotFound, NumberFormate, IO,
OutofMemory.
Errors : Virtual machine error: class not found, out of memory, no such method, illegal access to
private field, etc.
Runtime Exceptions :Programming errors that should be detected in testing: index out of bounds,
null pointer, illegal argument, etc.
Java Exception handling can be managed by five keywords:
 Try : The try block governs the statements that are enclosed within it and defines the
scope of exception handler associated with it. Try block follows catch or finally or
both.
 Catch: This is a default exception handler. since the exception class is the base class
for all the exception class, this handler id capable of catching any type of exception.
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The catch statement takes an Object of exception class as a parameter, if an exception is thrown
the statement in the catch block is executed. The catch block is restricted to the statements in
the proceeding try block only.
 Finally : when an exception is raised, the statement in the try block is ignored, some
times it is necessary to process certain statements irrespective of wheather an
exception is raised or not, the finally block is used for this purpose.
 Throw : The throw class is used to call exception explicitly. You may want to
throw an exception when the user enters a wrong login ID and pass word, you can
use throw statement to do so.
The throw statement takes an single argument, which is an Object of exception class.
Throw<throwable Instance>
If the Object does not belong to a valid exception class the compiler gives error.
 Throws :The throws statement species the list of exception that has thrown by a
method.
If a method is capable of raising an exception that is does not handle, it must specify the exception
has to be handle by the calling method, this is done by using the throw statement.
[<access specifier>] [<access modifier>] <return type> <method name> <arg-list>
[<exception-list>]
Multi Programming:
There are two types in multitasking .
Processed-based : heavy weight- allows you run two or more programs run concurrently.
Thread-based: Light weight- A Program can perform two or more tasks simultaneously.
Creating a thread:
By implementing the Runnable Interface.
By extending the thread Class.
Thread: can be defined as single sequential flow of control with in a program.
Thread Class : Java.lang.Threadclass is used to construct and access the individual threads
in a multithreaded application.
Syntax: Public Class <class name> extends Thread { }
The Thread class define several methods .
Getname() – obtain a thread name.
Getname() – obtain thread priority.
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Collections : A collection allows a group of objects to be treated as a single unit. collection
define a set of core Interfaces as follows.
Collection Map Hash Map class
Hash Table class
Set Hash set List
Array List
Sorted set Tree set Vector List
Linked List Sorted map Tree Map class
 Collection Interface :
 The Collection Interface is the root of collection hierarchy and is used for common
functionality across all collections.
 There is no direct implementation of Collection Interface.
 Set Interface: extends Collection Interface. The Class Hash set implements Set
Interface.
 Is used to represent the group of unique elements.
 Set stores elements in an unordered way but does not contain duplicate elements.
 Sorted set : extends Set Interface. The class Tree Set implements Sorted set Interface.
 It provides the extra functionality of keeping the elements sorted.
 It represents the collection consisting of Unique, sorted elements in ascending order.
 List :extends Collection Interface. The classes Array List, Vector List & Linked List
implements List Interface.
 Represents the sequence of numbers in a fixed order.
 But may contain duplicate elements.
 Elements can be inserted or retrieved by their position in the List using Zero based index.
 List stores elements in an ordered way.
 Map Interface: basic Interface.The classes Hash Map & Hash Table implements Map
interface.
 Used to represent the mapping of unique keys to values.
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 By using the key value we can retrive the values. Two basic operations are get( ) & put( ) .
 Sorted Map : extends Map Interface. The Class Tree Map implements Sorted Map
Interface.
 Maintain the values of key order.
 The entries are maintained in ascending order.
Collection classes:
Abstract Collection – implements most of collection Interfaces.
Abstract List – Extends Abstraction Collection.
Abstract sequential list – Linked List ; Array List ; Abstract Set ; Hash set ; Tree set
 HashSet : Implements Set Interface. HashSet hs=new
HashSet( );
 The elements are not stored in sorted order. hs.add(“m”);
 TreeSet : Implements Sorted set Interface. TreeSet ts=new
TreeSet( );
 The elements are stored in sorted ascending order. ts.add(“H”);
 Access and retrieval times are quit fast, when storing a large amount of data.
 Vector : Implements List Interface.
 Vector implements dynamic array. Vector v = new vector( );
 Vector is a growable object. V1.addElement(new
Integer(1));
 Vector is Synchronized, it can’t allow special characters and null values.
 All vector starts with intial capacity, after it is reached next time if we want to store
object in vector, the vector automatically allocates space for that Object plus extra room
for additional Objects.
 ArrayList : Implements List Interface.
 Array can dynamically increase or decrease size. ArrayList a1=new ArrayList( );
 Array List are ment for Random ascessing. A1.add(“a”);
 Array List are created with intial size, when the size is increased, the collection is
automatically enlarged. When an Objects are removed, the array may be shrunk.
 Linked List : Implements List Interface.
 Inserting or removing elements in the middle of the array. LinkedList l1=new LinkedList( );
 Linked list are meant for Sequential accessing. L1.add(“R”);
 Stores Objects in a separate link.
Map Classes:
Abstract Map; Hash Map ; Tree Map
 Hash Map: Implements Map Interface.Hashmap(), Hashmap(Map m), Hashmap(int
capacity)
 The Elements may not in Order.
 Hash Map is not synchronized and permits null values
 Hash Map is not serialized. Hashmap hm = new
HashMap( );
 Hash Map supports Iterators. hm.put(“Hari”,new
Double(11.9));
 Hash Table : Implements Map Interface.
 Hash Table is synchronized and does not permit null values.
 Hash Table is Serialized.
 Stores key/value pairs in Hash Table.
A Hash Table stores information by using a mechanism called hashing. In hashing the
informational content of a key is used to determine a unique value, called its Hash Code. The
Hash Code is then used as the index at which the data associated with the key is stored. The
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JAVA & J2EE
Transformation of the key into its Hash Code is performed automatically- we never see the
Hash Code. Also the code can’t directly index into h c.
 Tree Map : Implements Sorted Set Interface. TreeMap tm=new
TreeMap( );
 The elements are stored in sorted ascending order. tm.put( “Prasad”,new Double(74.6));
 Using key value we can retrieve the data.
 Provides an efficient means of storing key/value pairs in sorted order and allows rapid
retrivals.
 Iterator: Each of collection class provided an iterator( ).
By using this iterator Object, we can access each element in the collection – one at a time.
We can remove() ; it will come back. Hashnext( ) – go next; if it returns false –end of list.
How are memory leaks possible in Java
If any object variable is still pointing to some object which is of no use, then JVM will not
garbage collect that object and object will remain in memory creating memory leak
What are the differences between EJB and Java beans
the main difference is Ejb componenets are distributed which means develop once and run
anywhere.
java beans are not distributed. which means the beans cannot be shared .
What would happen if you say this = null
this will give a compilation error as follows
cannot assign value to final variable this
Will there be a performance penalty if you make a method synchronized? If so,
can you make any design changes to improve the performance
yes.the performance will be down if we use synchronization.
one can minimise the penalty by including garbage collection algorithm, which reduces the
cost of collecting large numbers of short- lived objects. and also by using Improved thread
synchronization for invoking the synchronized methods.the invoking will be faster.
How would you implement a thread pool
public class ThreadPool extends java.lang.Object implements ThreadPoolInt
This class is an generic implementation of a thread pool, which takes the following input
a) Size of the pool to be constructed
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JAVA & J2EE
b) Name of the class which implements Runnable (which has a visible default constructor)
and constructs a thread pool with active threads that are waiting for activation. once the
threads have finished processing they come back and wait once again in the pool.
This thread pool engine can be locked i.e. if some internal operation is performed on the
pool then it is preferable that the thread engine be locked. Locking ensures that no new
threads are issued by the engine. However, the currently executing threads are allowed to
continue till they come back to the passivePool
How does serialization work
Its like FIFO method (first in first out)
How does garbage collection work
There are several basic strategies for garbage collection: reference counting, mark-sweep,
mark-compact, and copying. In addition, some algorithms can do their job incrementally
(the entire heap need not be collected at once, resulting in shorter collection pauses), and
some can run while the user program runs (concurrent collectors). Others must perform an
entire collection at once while the user program is suspended (so-called stop-the-world
collectors). Finally, there are hybrid collectors, such as the generational collector employed
by the 1.2 and later JDKs, which use different collection algorithms on different areas of the
heap
How would you pass a java integer by reference to another function
Passing by reference is impossible in JAVA but Java support the object reference so.
Object is the only way to pass the integer by refrence.
What is the sweep and paint algorithm
The painting algorithm takes as input a source image and a list of brush sizes.
sweep algo is that it computes the arrangement of n lines in the plane ... a correct
algorithm,
Can a method be static and synchronized
no a static mettod can't be synchronised
Do multiple inheritance in Java
Its not possible directly. That means this feature is not provided by Java, but it can be
achieved with the help of Interface. By implementing more than one interface.
What is data encapsulation? What does it buy you
The most common example I can think of is a javabean. Encapsulation may be used by
creating 'get' and 'set' methods in a class which are used to access the fields of the object.
Typically the fields are made private while the get and set methods are public.
dEncapsulation can be used to validate the data that is to be stored, to do calculations
on data that is stored in a field or fields, or for use in introspection (often the case when
using javabeans in Struts, for instance).
What is reflection API? How are they implemented
Reflection pkg is used mainlyfor the purpose of getting the class name.
by useing the getName method we can get name of the class for particular application
Reflection is a feature of the Java programming language. It allows an executing Java
program to examine or "introspect" upon itself, and manipulate internal properties of the
program.
What are the primitive types in Java
According to Java in a Nutshell, 5th ed
boolean, byte, char, short, long float, double, int
Is there a separate stack for each thread in Java
No
What is heap in Java
JAVA is fully Object oriented language. It has two phases first one is Compilation phase and
second one is interpratation phase. The Compilation phase convert the java file to class file
(byte code is only readable format of JVM) than Intepratation phase interorate the class file
line by line and give the proper result.
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In Java, how are objects / values passed around
In Java Object are passed by reference and Primitive data is always pass by value
Do primitive types have a class representation
Primitive data type has a wrapper class to present.
Like for int - Integer for byte Byte, for long Long etc ...
How all can you free memory
With the help of finalize() method.
If a programmer really wants to explicitly request a garbage collection at some point,
System.gc() or Runtime.gc() can be invoked, which will fire off a garbage collection at that
time.
Does java do reference counting
It is more likely that the JVMs you encounter in the real world will use a tracing algorithm in
their garbage-collected heaps
What does a static inner class mean? How is it different from any other static
member
A static inner class behaves like any ``outer'' class. It may contain methods and fields.
It is not necessarily the case that an instance of the outer class exists even when we
have created an instance of the inner class. Similarly, instantiating the outer class does not
create any instances of the inner class.
The methods of a static inner class may access all the members (fields or methods)
of the inner class but they can access only static members (fields or methods) of the outer
class. Thus, f can access the field x, but it cannot access the field y.
How do you declare constant values in java
Using Final keyword we can declare the constant values
How all can you instantiate final members
Final member can be instantiate only at the time of declaration. null
How is serialization implemented in Java
A particular class has to implement an Interface java.io.Serializable for implementing
serialization.
When you have an object passed to a method and when the object is reassigned to a
different one, then is the original reference lost No Reference is not lost. Java always
passes the object by reference, now two references is pointing to the same object.
What are the different kinds of exceptions? How do you catch a Runtime
exception
There are 2 types of exceptions.
1. Checked exception
2. Unchecked exception.
Checked exception is catched at the compile time while unchecked exception is checked
at run time.
1.Checked Exceptions : Environmental error that cannot necessarily be detected by testing;
e.g. disk full, broken socket, database unavailable, etc.
2. Unchecked exception.
Errors : Virtual machine error: class not found, out of memory, no such method, illegal
access to private field, etc.
Runtime Exceptions :Programming errors that should be detected in testing: index out of
bounds, null pointer, illegal argument, etc.
Checked exceptions must be handled at compile time. Runtime exceptions do not need to
be. Errors often cannot be
What are the differences between JIT and HotSpot
The Hotspot VM is a collection of techniques, the most significant of which is called
"adaptive optimization.
The original JVMs interpreted bytecodes one at a time. Second-generation JVMs added a JIT
compiler, which compiles each method to native code upon first execution, then executes
the native code. Thereafter, whenever the method is called, the native code is executed.
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The adaptive optimization technique used by Hotspot is a hybrid approach, one that
combines bytecode interpretation and run-time compilation to native code.
Hotspot, unlike a regular JIT compiling VM, doesn't do "premature optimization"
What is a memory footprint? How can you specify the lower and upper limits of
the RAM used by the JVM? What happens when the JVM needs more memory?
when JVM needs more memory then it does the garbage collection, and sweeps all the
memory which is not being used.
What are the disadvantages of reference counting in garbage collection?
An advantage of this scheme is that it can run in small chunks of time closely interwoven
with the execution of the program. This characteristic makes it particularly suitable for real-
time environments where the program can't be interrupted for very long. A disadvantage of
reference counting is that it does not detect cycles. A cycle is two or more objects that refer
to one another, for example, a parent object that has a reference to its child object, which
has a reference back to its parent. These objects will never have a reference count of zero
even though they may be unreachable by the roots of the executing program. Another
disadvantage is the overhead of incrementing and decrementing the reference count each
time. Because of these disadvantages, reference counting currently is out of favor.
Is it advisable to depend on finalize for all cleanups
The purpose of finalization is to give an opportunity to an unreachable object to perform
any clean up before the object is garbage collected, and it is advisable
can we declare multiple main() methods in multiple classes. ie can we have each
main method in its class in our program?
YES
JDBC
How to Interact with DB?
Generally every DB vendor provides a User Interface through which we can easily
execute SQL query’s and get the result (For example Oracle Query Manager for Oracle, and
TOAD (www.quest.com) tool common to all the databases). And these tools will help DB
developers to create database. But as a programmer we want to interact with the DB
dynamically to execute some SQL queries from our application (Any application like C, C++,
JAVA etc), and for this requirement DB vendors provide some Native Libraries (Vendor
Specific) using this we can interact with the DB i.e. If you want to execute some queries on
Oracle DB, oracle vendor provides an OCI (Oracle Call Interface) Libraries to perform the
same.
About ODBC
What is ODBC
ODBC (Open Database Connectivity) is an ISV (Independent software vendor product)
composes of native API to connect to different databases through via a single API called
ODBC.
Open Database Connectivity (ODBC) is an SQL oriented application programming interface
developed by in collaboration with IBM and some other database vendors.
ODBC comes with Microsoft products and with all databases on Windows OS.
ODBC Architecture
13
“C”
function
calls
Front End
Application
Oracle ODBC
SQL server
ODBC
Sybase ODBC
Oracle
ODBC API
SP API
SQL
server
SybaseSP API
SP API
Oracle DSN
My DSN
SQL Server DSN
Sybase DSN
Our DSN
Oracle ODBC
SQL server ODBC
Sybase ODBC
Oracle
SQL
Server
Sybase

JAVA & J2EE
Advantages
• Single API (Protocol) is used to interact with any DB
• Switching from one DB to another is easy
• Doesn’t require any modifications in the Application when you want to shift from
one DB to other.
What for JDBC?
As we have studied about ODBC and is advantages and came to know that it provides
a common API to interact with any DB which has an ODBC Service Provider’s
Implementation written in Native API that can be used in your applications.
If an application wants to interact with the DB then the options which have been
explained up to now in this book are:
1. Using Native Libraries given by the DB vendor
2. Using ODBC API
And we have listed there Advantages and Disadvantages.
But if the application is a JAVA application then the above given options are not
recommended to be used due to the following reasons
1. Native Libraries given by DB vendor
a. Application becomes vendor dependent and
b. The application has to use JNI to interact with Native Lib which may cause serious
problem for Platform Independency in our applications.
2. And the second option given was using ODBC API which can solve the 1.a problem
but again this ODBC API is also a Native API, so we have to use JNI in our Java
applications which lead to the 1.b described problem.
And the answer for these problems is JDBC (Java Data Base Connectivity) which provides a
common Java API to interact with any DB.
What is JDBC
As explained above JDBC standards for Java Data Base Connectivity. It is a
specification given by Sun Microsystems and standards followed by X/Open SAG (SQL
Access Group) CLI (Call Level Interface) to interact with the DB.
Java programing language methods. The JDBC API provides database-independent
connectivity between the JAVA Applications and a wide range of tabular data bases. JDBC
technology allows an application component provider to:
• Perform connection and authentication to a database server
• Manage transactions
• Moves SQL statements to a database engine for preprocessing and
execution
• Executes stored procedures
• Inspects and modifies the results from SELECT statements
14

JAVA & J2EE
JDBC API
JDBC API is divided into two parts
1. JDBC Core API
2. JDBC Extension or Optional API
JDBC Core API (java.sql package)
This part of API deals with the following futures
1. Establish a connection to a DB
2. Getting DB Details
3. Getting Driver Details
4. maintaining Local Transaction
5. executing query’s
6. getting result’s (ResultSet)
7. preparing pre-compiled SQL query’s and executing
8. executing procedures & functions
JDBC Ext OR Optional API (javax.sql package)
This part of API deals with the following futures
1. Resource Objects with Distributed Transaction Management support
2. Connection Pooling.
These two parts of Specification are the part of J2SE and are inherited into J2EE i.e. this
specification API can be used with all the component’s given under J2SE and J2EE.
JDBC Architecture:
In the above show archetecture diagram the JDBC Driver forms an abstraction
layer between the JAVA Application and DB, and is implemented by 3rd
party vendors or a
DB Vendor. But whoever may be the vendor and what ever may be the DB we need not to
worry will just us JDCB API to give instructions to JDBC Driver and then it’s the
responsibility of JDBC Driver Provider to convert the JDBC Call to the DB Specific Call.
And this 3rd
party vendor or DB vendor implemented Drivers are classified into 4-Types
namely
Types Of Drivers
1. Type-1 (JDBC ODBC - Bridge Driver) JDBC-ODBC Bridge Driver
2. Type-2 (Java-Native API Driver) Native API Partly JAVA Driver (Thick
Driver)
3. Type-3 (Java Net Protocol Driver) Intermediate DataBase Access Server
4. Type-4 (Java Native Protocol driver) Pure JAVA Driver (Thin driver)
Type-1 _ JDBC ODBC Bridge Driver :
Since ODBC is written in C-language using pointers, so JAVA does’t
support pointers, a java program can’t communate directly with the DataBase. The JDBC-
ODBC bridge drivertransulates JDBC API calls to ODBC API calls.
Architecture
15
JDBC Application
JDBC Driver
Oracle DB MS SQL
Server DB
Sybase DB
JDB
C
API
S
P
A
PI
S
P
A
PI
SP
AP
I
JAVA
Application
JDBC
ODBC
Driver
Native
ODBC
Client
driver
Libraries
DBMS
Interface
client
libraries
DBMS
Interface
Server
Libraries
DBMS

JAVA & J2EE
This type of Driver is designed to convert the JDBC request call to ODBC call and ODBC
response call to JDBC call.
The JDBC uses this interface in order to communicate with the database, so neither
the database nor the middle tier need to be Java compliant. However ODBC binary code
must be installed on each client machine that uses this driver. This bridge driver uses a
configured data source.
Advantages
• Simple to use because ODBC drivers comes with DB installation/Microsoft front/back
office product installation
• JDBC ODBC Drivers comes with JDK software
Disadvantages
• More number of layers between the application and DB. And more number of API
conversions leads to the downfall of the performance.
• Slower than type-2 driver
Where to use?
This type of drivers are generaly used at the development time to test your application’s.
Because of the disadvantages listed above it is not used at production time. But if we are
not available with any other type of driver implementations for a DB then we are forced to
use this type of driver (for example Microsoft Access).
Examples of this type of drivers
JdbcOdbcDriver from sun
Sun’s JdbcOdbcDriver is one of type-1 drivers and comes along with sun j2sdk (JDK).
Setting environment to use this driver
1. Software
ODBC libraries has to be installed.
2. classpath
No additional classpath settings are required apart from the runtime jar
(c:j2sdk1.4jrelibrt.jar) which is defaultly configured.
3. Path
No additional path configuration is required.
How to use this driver
1. Driver class name  sun.jdbc.odbc.JdbcOdbcDriver
2. Driver URL  dbc:odbc:<DSN>
here <DSN> (Data Source Name) is an ODBC datasource name which is used by
ODBC driver to locate one of the ODBC Service Provider implementation API which
can in-turn connect to DB.
Steps to create <DSN>
1. run ‘Data Sources (ODBC)’ from Control PanalAdministrative Tools
(for Windows 2000 server/2000 professional/XP)
run ‘ODBC Data Sources’ from Control Panel
2. click on Add button available on the above displayed screen.
this opens a new window titled ‘Create New Data Source’ which displays all the available
DB’s lable DB’s ODBC drivers currently installed on your system.
3. Select the suitable driver and click on Finish
4. Give the required info to the driver (like username, service id etc)
Type-2 : Native API Partly JAVA Driver (Thick Driver) :
16

JAVA & J2EE
JDBC Database calls are translated into Vendor-specific API calls.
The database will process the request and send the results back through API to JDBC
Driver – this will translate the results to the JDBC standard and return them to the
Java application.
The Vendor specific language API must be installed on every client that runs the JAVA
application.
Architecture
This driver converts the JDBC call given by the Java application to a DB specific native call
(i.e. to C or C++) using JNI (Java Native Interface).
Advantages :Faster than the other types of drivers due to native library participation in
socket programing.
Disadvantage : DB spcifiic native client library has to be installed in the client machine.
• Preferablly work in local network environment because network service name
must be configured in client system
Where to use?
This type of drivers are suitable to be used in server side applications.
Not recommended to use with the applications using two tire model (i.e. client and
database layer’s) because in this type of model client used to interact with DB using the
driver and in such a situation the client system sould have the DB native library.
1. OCI 8 (Oracle Call Interface) for Oracle implemented by Oracle Corporation.
• Software: Oracle client software has to be installed in client machine
• classpath  %ORACLE_HOME%ora81jdbclibclasses111.zip
• path  %ORACLE_HOME%ora81bin
• Driver class name  oracle.jdbc.driver.OracleDriver
• Driver URL  jdbc:oracle:oci8:@TNSName
Note: TNS Names of Oracle is available in Oracle installed folder %ORACLE_HOME
%Ora81networkadmintnsnames.ora
2. Weblogic Jdriver for Oracle implemented by BEA Weblogic:
• Oracle client software has to be installed in client machine
• weblogicoic dll’s has to be set in the path
• classpath  d:beaweblogic700serverlibweblogic.jar
• path  %ORACLE_HOME%ora81bin;
d:beaweblogic700serverbin<subfolder><sub folder> is
o oci817_8 if you are using Oracle 8.1.x
o oci901_8 for Oracle 9.0.x
o oci920_8 for Oracle 9.2.x
• Driver class name  weblogic.jdbc.oci.Driver
• Driver URL  jdbc:weblogic:oracle:HostName
17
JDBC
Application
JDBC Type II
Driver
DBMS Client
libraries (native)
DBMS Server
libraries (native)
DBMS
JDBC
API
SP API
SP
N/W
Libra
ries
OCI
Libraries

JAVA & J2EE
Type-3 Intermediate DataBase Access Server :
Type-3 Driver uses an Intermediate(middleware) database driver
that has the ability to connect multiple JAVA clients to multiple database servers.
Client connect to the Databse server via an Intermediate server component (such as
listener) that acts as a gateway for multple database servers.
Bea weblogic includes Type-3 Driver.
Architecture :
This type of drivers responsibility is to convert JDBC call to Net protocol
(Middleware listener dependent) format and redirect the client request to Middleware
Listener and middleware listener inturn uses type-1, type-2 or type-4 driver to interact with
DB.
Advantages:
• It allows the flexibility on the architecture of the application.
• In absence of DB vendor supplied driver we can use this driver
• Suitable for Applet clients to connect DB, because it uses Java libraries for
communication between client and server.
Disadvantages:
• From client to server communication this driver uses Java libraries, but from server
to DB connectivity this driver uses native libraries, hence number of API conversion
and layer of interactions increases to perform operations that leads to performance
deficit.
• Third party vendor dependent and this driver may not provide suitable driver for all
DBs
Where to use?
• Suitable for Applets when connecting to databases
Examples of this type of drivers:
1. IDS Server (Intersolv) driver available for most of the Databases
• Software: IDS software required to be downloaded from the following URL
[ http://www.idssoftware.com/idsserver.html -> Export Evaluation ]
• classpath  C:IDSServerclassesjdk14drv.jar
• path 
• Driver class name  ids.sql.IDSDriver
• Driver URL  jdbc:ids://localhost:12/conn?dsn='IDSExamples'
Note: DSN Name must be created in ServerDSN
Type-4 Pure JAVA Driver (Thin driver) :
Type-4 Driver translates JDBC-API calls to direct network calls using
vendor specific networking protocols by making direct server connections with the
database.
Architecture
18
JDBC
Application
JDBC Type III
Driver
Middleware
Listener
DBMS Interface
Client
DBMS Interface
Server
Listener
JDBC
API
Net protocol
OCI Libraries
DBMS
DBMS API
DBMS Interface
Server Listener
JDBC
Application
JDBC Type IV
DriverJDBC
API
DBMS
API
DBMS
Native Protocol

JAVA & J2EE
This type of driver converts the JDBC call to a DB defined native protocol.
Advantage
• Type-4 driver are simple to deploy since there is No client native libraries required to
be installed in client machine
• Comes with most of the Databases
Disadvantages:
• Slower in execution compared with other JDBC Driver due to Java libraries are used
in socket communication with the DB
Where to use?
• This type of drivers are sutable to be used with server side applications, client side
application and Java Applets also.
1) Thin driver for Oracle implemented by Oracle Corporation
• classpath  %ORACLE_HOME%ora81jdbclibclasses111.zip
• Driver class name  oracle.jdbc.driver.OracleDriver
• Driver URL  jdbc:oracle:thin:@HostName:<port no>:<SID>
<port no>  1521
<SID> -> ORCL
2) MySQL Jconnector for MySQL database
• classpath  C:mysqlmysql-connector-java-3.0.8-stablemysql-
connector-java-3.0.8-stable-bin.jar
• Driver class name  com.mysql.jdbc.Driver
• Driver URL  jdbc:mysql:///test
Chapter 3 [JDBC Core API]
In this chapter we are going to discuss about 3 versions of JDBC: JDBC 1.0, 2.0
and 3.0
Q) How JDBC API is common to all the Databases and also to all drivers?
A) Fine! The answer is JDBC API uses Factory Method and Abstract Factory Design pattern
implementations to make API common to all the Databases and Drivers. In fact most of the
classes available in JDBC API are interfaces, where Driver vendors must provide
implementation for the above said interfaces.
Q) Then how JDBC developer can remember or find out the syntaxes of vendor
specific classes?
A) No! developer need not have to find out the syntaxes of vendor specific implementations
why because DriverManager is one named class available in JDBC API into which if you
register Driver class name, URL, user and password, DriverManager class in-turn brings us
one Connection object.
Q) Why most of the classes given in JDBC API are interfaces?
A) Why abstract class and abstract methods are?
19

JAVA & J2EE
Abstract class forces all sub classes to implement common methods whichever are required
implementations. Only abstract method and class can do this job. That’s’ why most part of
the JDBC API is a formation of interfaces.
JDBC API comes in 2 packages
java.sql.*
javax.sql.*
First of all I want to discuss briefly about all the list of interfaces and classes available in
java.sql. package
Interfaces index
Driver
Every JDBC Driver vendor must one sub class of this class for initial establishment of
Connections. DriverManager class need to be first registered with this class before
accepting URL and other information for getting DB connection.
Method index
• Connection connect(String url, Properties info)
This method takes URL argument and user name & password info as Properties
object
• boolean acceptURL(String url)
This method returns boolean value true if the given URL is correct, false if any wrong
in URL
• boolean jdbcComplaint()
JDBC compliance requires full support for the JDBC API and full support for SQL 92
Entry Level. It is expected that JDBC compliant drivers will be available for all the
major commercial databases.
Connection
Connection is class in-turn holds the TCP/IP connection with DB. Functions available in
this class are used to manage connection live-ness as long as JDBC application wants to
connect with DB. The period for how long the connection exists is called as Session. This
class also provides functions to execute various SQL statements on the DB. For instance the
operations for DB are mainly divided into 3 types
• DDL (create, alter, and drop)
• DML (insert, select, update and delete)
• DCL (commit, rollback) and also
• call function_name (or) call procedure_name
Method Index
• Statement createStatement()
• PreparedStatement prepareStatement(String preSqlOperation)
• CallableStatement prepareCall(String callToProc())
Statement
Statement class is the super class in its hierarchy. Provides basic functions to execute
query (select) and non-related (create, alter, drop, insert, update, delete) query
operations.
Method Index
• int executeUpdate(String sql)
This function accepts non-query based SQL operations; the return value int tells that how
many number of rows effected/updated by the given SQL operation.
• ResultSet executeQuery(String sql)
This function accepts SQL statement SELECT and returns java buffer object which contains
temporary instance of SQL structure maintaining all the records retrieved from the DB. This
object exists as long as DB connection exist.
• boolean execute()
This function accepts all SQL operations including SELECT statement also.
PreparedStatement
PreparedStatement class is sub classing from Statement class. While connection class
prepareStatement function is creating one new instance this class, function takes one String
20

JAVA & J2EE
argument that contains basic syntax of SQL operation represented with “?” for IN
parameter representation. In the further stages of the JDBC program, programmer uses
setXXX(int index, datatype identifier) to pass values into IN parameter and requests
exdcute()/ exuecteUpdate() call.
Method Index
• setInt(int index, int value) – similar functions are provided for all other primitive
parameters
• setString(int index, String value)
• setObject(int index, Object value)
• setBinaryStream(int index, InputStream is, int length)
CallableStatement
ResultSet ResultSetMetaData DatabaseMetaData
BLOB CLOB REF
SavePoint Struct
SQLInput SQLOutput SQLData
Class diagram required here
// TypeI DriverTest,java
package com.digitalbook.j2ee.jdbc;
import java.sql.*;
public class TypeIDriverTest
{
Connection con;
Statement stmt;
ResultSet rs;
public TypeIDriverTest ()
{
try {
// Load driver class into default ClassLoader
Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
// Obtain a connection with the loaded driver
con =DriverManager.getConnection ("jdbc:odbc:digitalbook","scott","tiger");
URL String - ("<protocol>:<subprotocol>:<subname>", " ", " " ); }
// create a statement
st=con.createStatement();
//execute SQL query
rs =st.executeQuery ("select ename,sal from emp");
System.out.println ("Name Salary");
System.out.println ("--------------------------------");
while(rs.next())
{
System.out.println (rs.getString(1)+" "+rs.getString(2));
}
rs.close ();
stmt.close ();
con.close ();
}
catch(Exception e)
{
e.printStackTrace ();
}
}
public static void main (String args[])
{
TypeIDriverTest demo=new TypeIDriverTest ();
}
}
// TypeIIDriverTest,java
21

JAVA & J2EE
package com.digitalbook.j2ee.jdbc;
import java.sql.*;
public class TypeIIDriverTest
{
Connection con;
Statement stmt;
ResultSet rs;
public TypeIIDriverTest ()
{
try {
// Load driver class into default ClassLoader
Class.forName ("oracle.jdbc.driver.OracleDriver");
// Obtain a connection with the loaded driver
con =DriverManager.getConnection ("jdbc:oracle:oci8:@digital","scott","tiger");
// create a statement
st=con.createStatement();
//execute SQL query
rs =st.executeQuery ("select ename,sal from emp");
System.out.println ("Name Salary");
System.out.println ("--------------------------------");
while(rs.next())
{
System.out.println (rs.getString(1)+" "+rs.getString(2));
}
rs.close ();
stmt.close ();
con.close ();
}
catch(Exception e)
{
e.printStackTrace ();
}
}
public static void main (String args[])
{
TypeIIDriverTest demo=new TypeIIDriverTest ();
}
}
Chapter 9 : [javax.sql package]
This package supplements the java.sql package and is included as a part of JDK 1.4
version. This package mainly provides following features:
1. DataSource interface was introduced in substitution to DriverManager class for
getting connection objects.
2. Connection Pooling
3. Distributed TX management
4. RowSets
Applications can directly use DataSource and RowSet API but connection pooling and
Distributed TX management APIs are used internally by the middle-tier infrastructure.
DataSource
DataSource is an interface. Driver vendor will provide implementation for this
interface (That means in case JDBC Driver Type II driver Oracle vendor for Oracle DB,
Intersolv in case of IDSServer). This object is used to obtain connections into any type of
JDBC program. Though DriverManager class is ideal for getting DB connection object, this
class provides some extra features over DriverManager class:
• Applications will obtain DB connection objects through via this factory class
• DataSource object will be registered into JNDI, hence any application connected in the
network can obtain this object by requesting JNDI API, DataSource class is having one
method called getConnection() geives one Connection object
22

JAVA & J2EE
• Application do not need to hard code a driver class
• Changes can be made to a data source properties, which means that it is not necessary
to make changes in application code when something about the data source or driver
changes
• Connection pooling and Distributed transactions are available through only the connection
obtained from this object. Connection obtained through DriverManager class do not have
this capability
DataSource interface is implemented by driver vendor. There are 3 types of
implementations available:
1. Basic Implementation- Produces a standard connection object.
2. Connection Pooling Implementation- Produces a connection object that
automatically participates in connection pooling. This implementation works with a
middle-tier connection pooling manager.
3. Distributed transaction implementation- Produces a connection object that may
be used for distributed transactions and almost always participates in connection
pooling. This implementation works with a middle-tier transaction manager and
almost always with a connection pool manager.
A driver that is accessed via a DataSource object does not register itself with the
DriverManager. Rather, a DataSource object is retrieved though a lookup operation and
then used to create a Connection object. With a basic implementation, the connection
obtained through a DataSource object is identical to a connection obtained through the
DriverManager facility.
Method Index
• Connection getConnection() – This function returns Connection object on demand of
this method.
• Connection getConnection(String user, String pass) – This function returns
Connection object on demand of this method by passing username and password.
Sub classes of this interface are
Type III Driver – IDSServer – Intersolv – ids.jdbc.IDSDataSource
Type III Driver – WebLogic – BEA – weblogic.jdbc.jta.DataSource – XA Support
Connection Pooling
Connections made via a DataSource object that is implemented to work with a
middle tier connection pool manager will participate in connection pooling. This can improve
the performance dramatically because creating a new connection is very expensive.
Connection Pool provides following features:
• Substantial improvement in the performance of DB application can be accomplished
by pre-caching the DB connection objects
• CPM supplied DB connections are remote enable
• CPM supplied DB connections are cluster aware
• CPM supplied DB connections supports DTM (distributed TXs)
• CPM supplied DB connections are not actual DB Connection objects, in turn they are
remote object, hence even though client closes DB connection using con.close() the
actual connection may not be closed instead RMI connection between client to CPM
are closed
• CPM supplied DB connection objects are serializable, hence client from any where in
the network can access DB connections
The classes and interfaces used for connection pooling are:
1. ConnectionPoolDataSource
2. PooledConnection
3. ConnectionEvent
4. ConnectionEventListener
Connection Pool Manager resided on middle tier system uses these classes and
interfaces behind the scenes. When the ConnectionPooledDataSource object is called on to
create PooledConnection object, the connection pool manager will register as a
ConnectionEventListener object with the new PooledConnection object. When the
23

JAVA & J2EE
connection is closed or there is an error, the connection pool manager (being listener) gets
a notification that includes a ConnectionEvent object.
Distributed Transactions
As with pooled connections, connections made via data source object that is
implemented to work with the middle tier infrastructure may participate in distributed
transactions. This gives an application the ability to involve data sources on multiple servers
in a single transaction.
The classes and interfaces used for distributed transactions are:
• XADataSource
• XAConnection
These interfaces are used by transaction manager; an application does not use them
directly.
The XAConnection interface is derived from the PooledConnection interface, so what
applies to a pooled connection also applies to a connection that is part of distributed
transaction. A transaction manager in the middle tier handles everything transparently. The
only change in application code is that an application cannot do anything that would
interfere with the transaction manager’s handling of the transaction. Specifically application
cannot call the methods Connection.commit or Connection.rollback and it cannot set the
connection to be in auto-commit mode.
An application does not need to do anything special to participate in a distributed
transaction. It simply creates connections to the data sources it wants to use via the
DataSource.getConnection method, just as it normally does. The transaction manager
manages the transaction behind the scenes. The XADataSource interface creates
XAConnection objects, and each XAConnection object creates an XAResource object that
the transaction manager uses to manage the connection.
Rowsets
The RowSet interface works with various other classes and interfaces behind the scenes.
These can be grouped into three categories.
1. Event Notification
o RowSetListener
A RowSet object is a JavaBeansTM
component because it has properties and participates in
the JavaBeans event notification mechanism. The RowSetListener interface is
implemented by a component that wants to be notified about events that occur to a
particular RowSet object. Such a component registers itself as a listener with a rowset via
the RowSet.addRowSetListener method.
o When the RowSet object changes one of its rows, changes all of it rows, or moves its
cursor, it also notifies each listener that is registered with it. The listener reacts by carrying
out its implementation of the notification method called on it.
o RowSetEvent
As part of its internal notification process, a RowSet object creates an instance of
RowSetEvent and passes it to the listener. The listener can use this RowSetEvent object to
find out which rowset had the event.
2. Metadata
RowSetMetaData
This interface, derived from the ResultSetMetaData interface, provides information about
the columns in a RowSet object. An application can use RowSetMetaData methods to find
out how many columns the rowset contains and what kind of data each column can contain.
The RowSetMetaData interface provides methods for setting the information about columns,
but an application would not normally use these methods. When an application calls the
RowSet method execute, the RowSet object will contain a new set of rows, and its
RowSetMetaData object will have been internally updated to contain information about the
new columns.
3. The Reader/Writer Facility
A RowSet object that implements the RowSetInternal interface can call on the
RowSetReader object associated with it to populate itself with data. It can also call on
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JAVA & J2EE
the RowSetWriter object associated with it to write any changes to its rows back to the
data source from which it originally got the rows. A rowset that remains connected to its
data source does not need to use a reader and writer because it can simply operate on
the data source directly.
RowSetInternal
By implementing the RowSetInternal interface, a RowSet object gets access to its internal
state and is able to call on its reader and writer. A rowset keeps track of the values in its
current rows and of the values that immediately preceded the current ones, referred to as
the original values. A rowset also keeps track of (1) the parameters that have been set for
its command and (2) the connection that was passed to it, if any. A rowset uses the
RowSetInternal methods behind the scenes to get access to this information. An application
does not normally invoke these methods directly.
RowSetReader
A disconnected RowSet object that has implemented the RowSetInternal interface can call
on its reader (the RowSetReader object associated with it) to populate it with data. When
an application calls the RowSet.execute method, that method calls on the rowset's reader
to do much of the work. Implementations can vary widely, but generally a reader makes a
connection to the data source, reads data from the data source and populates the rowset
with it, and closes the connection. A reader may also update the RowSetMetaData object
for its rowset. The rowset's internal state is also updated, either by the reader or directly by
the method RowSet.execute.
RowSetWriter
A disconnected RowSet object that has implemented the RowSetInternal interface can call
on its writer (the RowSetWriter object associated with it) to write changes back to the
underlying data source. Implementations may vary widely, but generally, a writer will do
the following:
 Make a connection to the data source
 Check to see whether there is a conflict, that is, whether a value that has been changed
in the rowset has also been changed in the data source
 Write the new values to the data source if there is no conflict
 Close the connection
The RowSet interface may be implemented in any number of ways, and anyone may write
an implementation. Developers are encouraged to use their imaginations in coming up with
new ways to use rowsets.
Type III Driver – WebLogic – BEA – weblogic.jdbc.common.internal.ConnectionPool
Type III Driver – WebLogic – BEA – weblogic.jdbc.connector.internal.ConnectionPool
Type II & IV driver – Oracle DB - Oracle –
JDBC:
There are three types of statements in JDBC
Create statement : Is used to execute single SQL statements.
Prepared statement: Is used for executing parameterized quaries. Is ued to run pre-
compiled SEQL Stat.
Callable statement: Is used to execute stored procedures.
Stored Procedures: Is a group of SQL statements that perform a logical unit and performs a
particular task.
Are used to encapsulate a set operations or queries t execute on data.
execute() – returns Boolean value
executeupdate( ) – returns resultset Object
executeupdate( ) – returns integer value
Loading the Driver:
Class.forName(“sun.jdbc.odbc.jdbcodbc”);
Conn=DriverManager.getConnection(“jdbc:odbc:dsn”, “username”, “password”);
( ORACLE Driver )
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JAVA & J2EE
Class.forName(“Oracle:jdbc:driver.OracleDriver”);
Conn=DriverManager.getConnection(“jdbc:oracle:thin:@192.168.1.105:1521:dbn”,
username”, “password”);
Data base connection:
Public static void main(String args[]);
Connection con;
Statement st;
Resultset rs;
try { // Getting all rows from Table
Clas.forName(“sun.jdbc.odbc.jdbcodbc”);
Conn=DriverManager.getConnction(“jdbc.odbc.dsn”, “username” , ”password”);
st = con.createstatement( );
rs = st.executestatement(“SELECT * FROM mytable”);
while(rs.next());
{
String s= rs.getString(1); or rs.setString(“COL_A”);
int i = rs. getInt(2);
Float f = rs.getfloat(3);
Process(s,i,f);
}
catch(SQLException e)
{ }
//Getting particular rows from Table
rs = st.executequery(“SELECT * FROM mytable WHERE COL A = “Prasad”);
while(rs.next( ));
{
String s = rs.getString(1);
Int i = rs.getint(2);
Float f = rs.getfloat(3);
Process(s,i,f);
}
Catch(SQLException e); { }
//updating a row from table.
try {
int numupdated = st.executeupdate(“UPDATE mytable SET COL_A = “prasad” WHERE
COL_B=”746”);
rs = st.executeupdate();
conn.close(); }
catch(SQLExceptione); { }
// Receiving rows from table
try {
st = con.preparedstatement( );
rs = st.execurtestatement(“SELECT * FROM mytable SET COL_A=?’);
int colunm=1;
rs.setString(colunm,”hari”);
rs = st.executeQuery( );
//update rwo from table
int numupdated = st.executeupdate(“UPDATE mytable SET COL_A =? WHERE COL_B=?”);
int column=1;
rs.setString(colunm,”Prasad”);
int column=2;
rs.setString(column,”746”);
int numupdated = st.executeupdate( );
} catch(SqlException e); { }
//callable statement
try {
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JAVA & J2EE
cst = con.preparecall(“{call add1(??,??)}”);
cst.setint(1,a);
cst.setint(2,b);
cst.registerOurPrameter(1,types,INTEGER);
cst.executeQuery( );
System.out.println(“rs.getString( )”); }
Connection Pool with webLogic server :
You can connect the database in your app using :
Class.forName(“weblogic:jdbc:oci:Driver”).newInstance();
Java.sql.Connection conn = Driver.connect(“jdbc:weblogic:Oracle:dbn”, ”username”,
“password”);
( Or )
java.util.Properties prop = new java.util.Properties( );
prop.put(“user”, “hari”);
prop.put(“password”,”prasad”);
java.sql.Driver d = (java.sql.Driver)Class.forName(“weblogic.jdbc.oci.Driver”).newInstance( );
java.sql.Connection conn = d.connect(“jdbc:weblogic:Oracle:dbn”, prop);
public static void main(String args[]) throws Exception
{
java.sql.Connection con=null;
java.sql.satement st =null;
try {
context ctx=null;
Hashtable ht = new Hashtable( );
ht.put(Context.INTIAL_CONTEXT_FACTORY,”weblogic:jndi:WLInitialContextFACTORY”);
ht.put(Context_PROVIDER_URL,”t3://Localhost:7001”);
//get a context from JNDI lookup
ctx = newIntialContext( ):
java.sql.Datasourse ds =(java.sql.DataSource)ctx.lookup(“OraclegbJNDI”);
con =ds.getConnection( );
System.out.Println(“Making Connection……”);
st = conn.createstatement( );
}
finally {
try {
if(stmt !=null)
stmt.close( );
if(stmt !=null)
con.close( ); }
What is a transaction
transaction is collection of logical operation that perform a task
Transaction should ACID properties.
A for Automicity
C for Consistency
I for Isolation
D for Durability.
A transaction can be termed as any operation such as storing, retrieving, updating or
deleting records in the table that hits the database.
What is the purpose of setAutoCommit( )
It is set as
ConnectionObject.setAutoComit();
after any updates through the program cannot be effected to the database.We have commit
the transctions .For this puprpose we can set AutoCommit flag to Connection Object.
What are the three statements in JDBC & differences between them
which is used to run simple sql statements like select and update
2. PrepareStatment is used to run Pre compiled sql.
3. CallableStatement is used to execute the stored procedures.
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What is stored procedure. How do you create stored procedure ?
Stored procedures is a group of SQL statements that performs a logical unit and
performs a particular task.
Stored procedures are used to encapsulate a set of operations or queries to
execute on data.
Stored Procedure is a stored program in database, PL/SQL program is a Stored
Procedure. Stored Procedures can be called from java by CallableStatement
A precompiled collection of SQL statements stored under a name and processed as a
unit.
Stored procedures can:
1.Accept input parameters and return multiple values in the form of output parameters to
the calling procedure or batch.
2.Contain programming statements that perform operations in the database, including
calling other procedures.
3.Return a status value to a calling procedure or batch to indicate success or failure (and
the reason for failure).
What are batch updates?
Batch Update facility allows multiple update operations to be submitted to a database for
processing at once. Using batch updates will improve the performance.
What is the difference between Resultset and Rowset
A RowSet is a disconnected, serializable version of a JDBC ResultSet.
The RowSet is different than other JDBC interfaces in that you can write a RowSet to be
vendor neutral. A third party could write a RowSet implementation that could be used with
any JDBC-compliant database. The standard implementation supplied by Sun uses a
ResultSet to read the rows from a database and then stores those rows as Row objects in a
Vector inside the RowSet. In fact, a RowSet implementation could be written to get its data
from any source. The only requirement is that the RowSet acts as if it was a ResultSet. Of
course, there is no reason that a vendor couldn't write a RowSet implementation that is
vendor specific.
The standard implementations have been designed to provide a fairly good range
of functionality. The implementations provided are:
CachedRowSetImpl - This is the implementation of the RowSet that is closest to the
definition of RowSet functionality that we discussed earlier. There are two ways to load this
RowSet. The execute ( ) method will load the RowSet using a Connection object. The
populate( ) method will load the RowSet from a previously loaded ResultSet.
WebRowSetImpl - This is very similar to the CachedRowSetImpl (it is a child class) but it
also includes methods for converting the rows into an XML document and loading the
RowSet with an XML document. The XML document can come from any Stream or
Reader/Writer object. This could be especially useful for Web Services.
JdbcRowSetImpl - This is a different style of implementation that is probably less useful
in normal circumstances. The purpose of this RowSet is to make a ResultSet look like a
JavaBean. It is not serializable and it must maintain a connection to the database.
The remaining two implementations are used with the first three implementations:
FilteredRowSetImpl - This is used to filter data from an existing RowSet. The filter will
skip records that don't match the criteria specified in the filter when a next() is used on the
RowSet.
JoinRowSetImpl - This is used to simulate a SQL join command between two or more
RowSet objects.
What are the steps for connecting to the database using JDBC
Using DriverManager:
1. Load the driver class using class.forName(driverclass) and class.forName() loads the
driver class and passes the control to DriverManager class
2. DriverManager.getConnection() creates the connection to the databse
Using DataSource.
DataSource is used instead of DriverManager in Distributed Environment with the help of
JNDI.
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1. Use JNDI to lookup the DataSource from Naming service server.
3. DataSource.getConnection method will return Connection object to the database
What is Connection Pooling ?
Connection pooling is a cache of data base connections that is maintained in memory ,
so that the connections may be reuse.
Connection pooling is a place where a set of connections are kept and are used by the
different programers with out creating conncections to the database(it means there is a
ready made connection available for the programmers where he can use). After using the
connection he can send back that connection to the connection pool. Number of connections
in connection pool may vary.
How do you implement Connection Pooling
Connection Pooling can be implemented by the following way.
* A javax.sql.ConnectionPoolDataSource interface that serves as a resource
manager connection factory for pooled java.sql.Connection objects. Each database vendors
provide the implementation for that interface.
For example, the oracle vendors implementation is as follows:
oracle.jdbc.pool.oracleConnectionPoolDataSource Class.
• A javax.sql.PooledConnection interface encapsulates the physical connection for the
database. Again, the vendor provides the implementation.
What Class.forName( ) method will do
Class.forName() is used to load the Driver class which is used to connect the
application with Database. Here Driver class is a Java class provided by Database vendor.
What is the difference between JDBC 1.0 and JDBC 2.0
The JDBC 2.0 API includes many new features in the java.sql package as well as the
new Standard Extension package, javax.sql. This new JDBC API moves Java applications
into the world of heavy-duty database computing. New features in the java.sql package
include support for SQL3 data types, scrollable result sets, programmatic updates, and
batch updates. The new JDBC Standard Extension API, an integral part of Enterprise
JavaBeans (EJB) technology, allows you to write distributed transactions that use
connection pooling, and it also makes it possible to connect to virtually any tabular data
source, including files and spread sheets.
The JDBC 2.0 API includes many new features like
1. Scrollable result sets
2. Batch updates
3. Connection Pooling
4. Distributed transactions
5. set autocomit ( )
What is JDBC?
JDBC is a layer of abstraction that allows users to choose between databases. It allows you
to change to a different database engine and to write to a single API. JDBC allows you to
write database applications in Java without having to concern yourself with the underlying
details of a particular database.
What are the two major components of JDBC?
One implementation interface for database manufacturers, the other implementation
interface for application and applet writers.
What is JDBC Driver interface?
The JDBC Driver interface provides vendor-specific implementations of the abstract classes
provided by the JDBC API. Each vendors driver must provide implementations of the
java.sql.Connection,Statement,PreparedStatement, CallableStatement, ResultSet and
Driver.
What are the common tasks of JDBC?
Create an instance of a JDBC driver or load JDBC drivers through jdbc.drivers
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Register a driver
Specify a database
Open a database connection
Submit a query
Receive results
What packages are used by JDBC?
There are 8 packages: java.sql.Driver, Connection,Statement, PreparedStatement,
CallableStatement, ResultSet, ResultSetMetaData, DatabaseMetaData.
What are the flow statements of JDBC?
A URL string -->getConnection-->DriverManager-->Driver-->Connection-->Statement--
>executeQuery-->ResultSet.
1). Register the Driver
2) load the Driver
3)get the connection
4) create the statement
5) Execute the query
6) fetch the results with ResultSet
What are the steps involved in establishing a connection?
This involves two steps: (1) loading the driver and (2) making the connection.
How can you load the drivers?
Loading the driver or drivers you want to use is very simple and involves just one line of
code. If, for example, you want to use the JDBC-ODBC Bridge driver, the following code will
load it:
Eg. Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Your driver documentation will give you the class name to use. For instance, if the class
name is jdbc.DriverXYZ , you would load the driver with the following line of code:
E.g. Class.forName("jdbc.DriverXYZ");
What Class.forName will do while loading drivers?
It is used to create an instance of a driver and register it with the DriverManager.
When you have loaded a driver, it is available for making a connection with a DBMS.
How can you make the connection?
In establishing a connection is to have the appropriate driver connect to the DBMS. The
following line of code illustrates the general idea:
E.g.
String url = "jdbc:odbc:Fred";
Connection con = DriverManager.getConnection(url, "Fernanda", "J8");
How can you create JDBC statements?
A Statement object is what sends your SQL statement to the DBMS. You simply
create a Statement object and then execute it, supplying the appropriate execute method
with the SQL statement you want to send. For a SELECT statement, the method to use is
executeQuery. For statements that create or modify tables, the method to use is
executeUpdate. E.g. It takes an instance of an active connection to create a Statement
object. In the following example, we use our Connection object con to create the Statement
object stmt :
Statement stmt = con.createStatement();
How can you retrieve data from the ResultSet?
First JDBC returns results in a ResultSet object, so we need to declare an instance of
the class ResultSet to hold our results. The following code demonstrates declaring the
ResultSet object rs.
E.g.
ResultSet rs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
Second:
String s = rs.getString("COF_NAME");
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The method getString is invoked on the ResultSet object rs , so getString will retrieve (get)
the value stored in the column COF_NAME in the current row of rs
What are the different types of Statements?
1. Create Statement : For Simple statement used for static query.
2.Prepared Statement :For a runtime / dynamic query .Where String is a dynamic query
you want to execute
3. Callable Statement (Use prepareCall) : //For Stored procedure Callable statement,
where sql is stored procedure.
try
{
Connection conn = DriverManager.getConnection("URL",'USER"."PWD");
Statement stmt = conn.createStatement();
PreparedStatement pstmt = conn.prepareStatement(String sql);
CallableStatement cstmt = conn.prepareCall(String sql);
}
catch (SQLException ee)
{
ee.printStackTrace();
}
Don't forget all the above statements will throw the SQLException, so we need to use try
catch for the same to handle the exception.
How can you use PreparedStatement?
This special type of statement is derived from the more general class, Statement. If you
want to execute a Statement object many times, it will normally reduce execution time to
use a PreparedStatement object instead. The advantage to this is that in most cases, this
SQL statement will be sent to the DBMS right away, where it will be compiled. As a result,
the PreparedStatement object contains not just an SQL statement, but an SQL statement
that has been precompiled. This means that when the PreparedStatement is executed, the
DBMS can just run the PreparedStatement 's SQL statement without having to compile it
first.
E.g. PreparedStatement updateSales = con.prepareStatement("UPDATE COFFEES SET
SALES = ? WHERE COF_NAME LIKE ?");
How to call a Stored Procedure from JDBC?
The first step is to create a CallableStatement object. As with Statement an and
PreparedStatement objects, this is done with an open Connection object. A
CallableStatement object contains a call to a stored procedure;
E.g.
CallableStatement cs = con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();
How to Retrieve Warnings?
SQLWarning objects are a subclass of SQLException that deal with database access
warnings. Warnings do not stop the execution of an application, as exceptions do; they
simply alert the user that something did not happen as planned. A warning can be reported
on a Connection object, a Statement object (including PreparedStatement and
CallableStatement objects), or a ResultSet object. Each of these classes has a getWarnings
method, which you must invoke in order to see the first warning reported on the calling
object
E.g.
SQLWarning warning = stmt.getWarnings();
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if (warning != null) {
while (warning != null) {
System.out.println("Message: " + warning.getMessage());
System.out.println("SQLState: " + warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
warning = warning.getNextWarning();
}
}
How to Make Updates to Updatable Result Sets?
Another new feature in the JDBC 2.0 API is the ability to update rows in a result set using
methods in the Java programming language rather than having to send an SQL command.
But before you can take advantage of this capability, you need to create a ResultSet object
that is updatable. In order to do this, you supply the ResultSet constant
CONCUR_UPDATABLE to the createStatement method.
E.g.
Connection con = DriverManager.getConnection("jdbc:mySubprotocol:mySubName");
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = ("SELECT COF_NAME, PRICE FROM COFFEES");
SERVLETS
Web Components
••ServletsServlets
••Java Server Pages (JSP)Java Server Pages (JSP)
••Tags and Tag LibrariesTags and Tag Libraries
What’s a Servlet?
••Java’s answer to CGI programmingJava’s answer to CGI programming
••Program runs on Web server and builds pages on the flyProgram runs on Web server and builds pages on the fly
••When would you use servlets?When would you use servlets?
–Data changes frequently e.g. weather-reports
–Page uses information from databases e.g. on-line stores
–Page is based on user-submitted data e.g search engines
–Data changes frequently e.g. weather-reports
–Page uses information from databases e.g. on-line stores
–Page is based on user-submitted data e.g search engines
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SERVLETS
1. What is the servlet?
Servlets are modules that extend request/response-oriented servers, such as Java-enabled
web servers. For example, a servlet may be responsible for taking data in an HTML order-
entry form and applying the business logic used to update a company's order database.
2. What are the uses of Servlets?
A servlet can handle multiple requests concurrently, and can synchronize requests. This
allows servlets to support systems such as on-line conferencing. Servlets can forward
requests to other servers and servlets. Thus servlets can be used to balance load among
several servers that mirror the same content, and to partition a single logical service over
several servers, according to task.
3. What is the difference between JSP and SERVLETS
servlet : it is a webcomponet which will handle the request as well as it will give the
response in particular display format.i.e it will perform developers tasks and designer's
tasks.
JSP: : it is purely for display purpose.it wil internally create a sevlet for perfoming
developers activities.
4. What are the advantages using servlets than using CGI?
Servlets provide a way to generate dynamic documents that is both easier to write and
faster to run. It is efficient, convenient, powerful, portable, secure and inexpensive.
Servlets also address the problem of doing server-side programming with platform-specific
APIs. They are developed with Java Servlet API, a standard Java extension.
5. What is the difference between servlets and applets?
Servlets are to servers. Applets are to browsers. Unlike applets, however, servlets have no
graphical user interface.
6. What is the difference between GenericServlet and HttpServlet?
GenericServlet is for servlets that might not use HTTP, like for instance FTP service.As of
only Http is implemented completely in HttpServlet. The GenericServlet has a service()
method that gets called when a client request is made. This means that it gets called by
both incoming requests and the HTTP requests are given to the servlet as they are.
GenericServlet belongs to javax.servlet package
GenericServlet is an abstract class which extends Object and implements Servlet,
ServletConfig and java.io.Serializable interfaces.
The direct subclass to GenericServlet is HttpServlet.It is a protocol-independent servlet
7. What are the differences between GET and POST service methods?
A GET request is a request to get a resource from the server. Choosing GET as the
"method" will append all of the data to the URL and it will show up in the URL bar of your
browser. The amount of information you can send back using a GET is restricted as URLs
can only be 1024 characters. A POST request is a request to post (to send) form data to a
resource on the server. A POST on the other hand will (typically) send the information
through a socket back to the webserver and it won't show up in the URL bar. You can send
much more information to the server this way - and it's not restricted to textual data either.
It is possible to send files and even binary data such as serialized Java objects!
8. What is the servlet life cycle?
Each servlet has the same life cycle:
A server loads and initializes the servlet (init())
The servlet handles zero or more client requests (service())
The server removes the servlet (destroy()) (some servers do this step only when they shut
down)
In Servlet life cycles are,
init(),services(),destory().
If init() executed at the time of servlet class loading.And init() executed only for first user.
If services() are both for get and post methods.
So if u want to use post method in html page,we use doPost() or services() in servlet class.
if want to use get methods in html page,we can use doGet() or services() in servlet calss.
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Finally destory() is used to free the object.
9. What is the difference between ServletContext and ServletConfig?
Both are interfaces.
Servlet Config():The servlet engine implements the ServletConfig interface in order to
pass configuration information to a servlet. The server passes an object that implements
the ServletConfig interface to the servlet's init() method.
A ServletConfig object passes configuration information from the server to a servlet.
ServletConfig also includes ServletContext object.
Servlet Context(): The ServletContext interface provides information to servlets regarding
the environment in which they are running. It also provides standard way for servlets to
write events to a log file.
ServletContext defines methods that allow a servlet to interact with the host server. This
includes reading server-specific attributes, finding information about particular files located
on the server, and writing to the server log files. I f there are several virtual servers
running, each one may return a different ServletContext
10. Can I invoke a JSP error page from a servlet?
Yes, you can invoke the JSP error page and pass the exception object to it from within a
servlet. The trick is to create a request dispatcher for the JSP error page, and pass the
exception object as a javax.servlet.jsp.jspException request attribute. However, note that
you can do this from only within controller servlets.
11. If your servlet opens an OutputStream or PrintWriter, the JSP engine will throw
the following translation error:
java.lang.IllegalStateException: Cannot forward as OutputStream or Writer has already
been obtained
12. The following code snippet demonstrates the invocation of a JSP error page from
within a controller servlet:
protected void sendErrorRedirect(HttpServletRequest request,
HttpServletResponse response, String errorPageURL, Throwable e) throws
ServletException, IOException {
request.setAttribute ("javax.servlet.jsp.jspException", e);
getServletConfig().getServletContext().
getRequestDispatcher(errorPageURL).forward(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
{
try {
// do something
} catch (Exception ex) {
try {
sendErrorRedirect(request,response,"/jsp/MyErrorPage.jsp",ex);
} catch (Exception e) {
e.printStackTrace();
}
} }
13. Can I just abort processing a JSP?
Yes.Because your JSP is just a servlet method,you can just put (whereever necessary) a <
% return; %>
14. What is a better approach for enabling thread-safe servlets and JSPs?
SingleThreadModel Interface or Synchronization?
Although the SingleThreadModel technique is easy to use, and works well for low volume
sites, it does not scale well. If you anticipate your users to increase in the future, you may
be better off implementing explicit synchronization for your shared data. The key however,
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JAVA & J2EE
is to effectively minimize the amount of code that is synchronzied so that you take
maximum advantage of multithreading.
Also, note that SingleThreadModel is pretty resource intensive from the server's
perspective. The most serious issue however is when the number of concurrent requests
exhaust the servlet instance pool. In that case, all the unserviced requests are queued until
something becomes free - which results in poor performance. Since the usage is non-
deterministic, it may not help much even if you did add more memory and increased the
size of the instance pool.
15. If you want a servlet to take the same action for both GET and POST request, what
should you do?
Simply have doGet call doPost, or vice versa.
16. Which code line must be set before any of the lines that use the PrintWriter?
setContentType() method must be set before transmitting the actual document.
17. How HTTP Servlet handles client requests?
An HTTP Servlet handles client requests through its service method. The service method
supports standard HTTP client requests by dispatching each request to a method designed
to handle that request.
18. What is the Servlet Interface?
The central abstraction in the Servlet API is the Servlet interface. All servlets implement
this interface, either directly or, more commonly, by extending a class that implements it
such as HttpServlet.
Servlets-->Generic Servlet-->HttpServlet-->MyServlet.
The Servlet interface declares, but does not implement, methods that manage the servlet
and its communications with clients. Servlet writers provide some or all of these methods
when developing a servlet.
19. When a servlet accepts a call from a client, it receives two objects. What are they?
ServeltRequest: which encapsulates the communication from the client to the server.
ServletResponse: which encapsulates the communication from the servlet back to the
client.
ServletRequest and ServletResponse are interfaces defined by the javax.servlet package.
20. What information that the ServletRequest interface allows the servlet access to?
Information such as the names of the parameters passed in by the client, the protocol
(scheme) being used by the client, and the names of the remote host that made the
request and the server that received it. The input stream, ServletInputStream.Servlets use
the input stream to get data
from clients that use application protocols such as the HTTP POST and PUT methods.
21. What information that the ServletResponse interface gives the servlet methods
for replying to the client?
It Allows the servlet to set the content length and MIME type of the reply. Provides an
output stream, ServletOutputStream and a Writer through which the servlet can send the
reply data.
22. Difference between single thread and multi thread model servlet
A servlet that implements SingleThreadModel means that for every request, a single servlet
instance is created. This is not a very scalable solution as most web servers handle
multitudes of requests. A multi-threaded servlet means that one servlet is capable of
handling many requests which is the way most servlets should be implemented.
a. A single thread model for servlets is generally used to protect sensitive data ( bank account
operations ).
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JAVA & J2EE
b. Single thread model means instance of the servlet gets created for each request recieved.
Its not thread safe whereas in multi threaded only single instance of the servlet exists for
what ever # of requests recieved. Its thread safe and is taken care by the servlet container.
c. A servlet that implements SingleThreadModel means that for every request, a single servlet
instance is created. This is not a very scalable solution as most web servers handle
multitudes of requests. A multi-threaded servlet means that one servlet is capable of
handling many requests which is the way most servlets should be implemented.
A single thread model for servlets is generally used to protect sensitive data ( bank account
operations ).
23. What is servlet context and what it takes actually as parameters?
Servlet context is an object which is created as soon as the Servlet gets initialized.Servlet context
object is contained in Servlet Config. With the context object u can get access to specific
resource (like file) in the server and pass it as a URL to be displayed as a next screen with the
help of RequestDispatcher
eg :-
ServletContext app = getServletContext();
RequestDispatcher disp;
if(b==true)
disp = app.getRequestDispatcher
("jsp/login/updatepassword.jsp");
else
disp = app.getRequestDispatcher
("jsp/login/error.jsp");
this code will take user to the screen depending upon the value of b.
in ServletContext u can also get or set some variables which u would
like to retreive in next screen.
eg
context.setAttribute("supportAddress", "temp@temp.com");
Better yet, you could use the web.xml context-param element to
designate the address, then read it with the getInitParameter method
of ServletContext.
24. Can we call destroy() method on servlets from service method?
destroy() is a servlet life-cycle method called by servlet container to kill the instance of the
servlet.
"Yes". You can call destroy() from within the service(). It will do whatever logic you have in
destroy() (cleanup, remove attributes, etc.) but it won't "unload" the servlet instance itself.
That can only be done by the container
25. What is the use of ServletConfig and ServletContext..?
An interface that describes the configuration parameters for a servlet. This is passed to the
servlet when the web server calls its init() method. Note that the servlet should save the
reference to the ServletConfig object, and define a getServletConfig() method to return it
when asked. This interface defines how to get the initialization parameters for the servlet
and the context under which the servlet is running.
An interface that describes how a servlet can get information about the server in which
it is running. It can be retrieved via the getServletContext() method of the ServletConfig
object.
26. What is difference between sendRedirect() and forward()..? Which one is faster
then other and which works on server?
When you invoke a forward request, the request is sent to another resource on the server,
without the client being informed that a different resource is going to process the request.
This process occurs completely with in the web container. When a sendRedirtect method is
invoked, it causes the web container to return to the browser indicating that a new URL
should be requested. Because the browser issues a completely new request any object that
are stored as request attributes before the redirect occurs will be lost. This extra round trip
a redirect is slower than forward.
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JAVA & J2EE
27. do we have a constructor in servlet ? can we explictly provide a constructor in
servlet programme as in java program ?
We can have a constructor in servlet .
28. How to communicate between two servlets?
Two ways:
a. Forward or redirect from one Servlet to another.
b. Load the Servlet from ServletContext and access methods.
29. How to get one Servlet's Context Information in another Servlet?
Access or load the Servlet from the Servlet Context and access the Context Information
37

JAVA & J2EE
JSP (JavaServer Pages)
Why JSP Technology?
•Servlets are good at running logic
–Not so good at producing large amounts of output
–out.write() is ugly
•JSP pages are great at producing lots of textual output
–Not so good at lots of logic
–<% %> is ugly
What is the difference between include directive & jsp:include action
include directive (): if the file includes static text
if the file is rarely changed (the JSP engine may not recompile the JSP if this type of
included file is modified)
if you have a common code snippet that you can reuse across multiple pages (e.g. headers
and footers)
jsp:include :
for content that changes at runtime
to select which content to render at runtime (because the page and src attributes can take
runtime expressions)
for files that change often
JSP:includenull
What are Custom tags. Why do you need Custom tags. How do you create Custom
tag
1) Custom tags are those which are user defined.
2) Inorder to separate the presentation logic in a separate class rather than keeping in jsp
page we can use custom tags.
3)
Step 1 : Build a class that implements the javax.servlet.jsp.tagext.Tag
interface as follows. Compile it and place it under the web-inf/classes
directory (in the appropriate package structure).
package examples;
import java.io.*; //// THIS PROGRAM IS EVERY TIME I MEAN WHEN
U REFRESH THAT PARTICULAR CURRENT DATE THIS CUSTOM TAG WILL DISPLAY
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
public class ShowDateTag implements Tag {
private PageContext pageContext;
private Tag parent;
public int doStartTag() throws JspException {
return SKIP_BODY; }
public int doEndTag() throws JspException {
try {
pageContext.getOut().write("" + new java.util.Date());
} catch (IOException ioe) {
throw new JspException(ioe.getMessage());
}
return EVAL_PAGE; }
public void release() {
}
public void setPageContext(PageContext page) {
this.pageContext = page;
}
public void setParent(Tag tag) {
this.parent = tag;
}
public Tag getParent() {
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JAVA & J2EE
return this.parent; }
}
Step 2:Now we need to describe the tag, so create a file called taglib.tld and place it under
the web-inf directory."http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd"> 1.0 1.1
myTag
http://www.mycompany.com/taglib My own tag library showDate
examples.ShowDateTag Show the current date Step 3 : Now we need to tell the web
application where to find the custom tags, and how they will be referenced from JSP pages.
Edit the web.xml file under the web-inf directory and insert the following XML
fragement.
http://www.mycompany.com/taglib /WEB-INF/taglib.tld
Step 4 : And finally, create a JSP page that uses the custom tag.Now restart the server
and call up the JSP page! You should notice that every time the page is requested, the
current date is displayed in the browser. Whilst this doesn't explain what all the various
parts of the tag are
for (e.g. the tag description, page context, etc) it should get you going. If you use the
tutorial (above) and this example, you should be able to grasp what's going on! There are
some methods in context object with the help of which u can get the server (or servlet
container) information.
Apart from all this with the help of ServletContext u can implement ServletContextListener
and then use the get-InitParametermethod to read context initialization parameters as the
basis of data that will be made available to all servlets and JSP pages.
What are the implicit objects in JSP & differences between them
There are nine implicit objects in JSP.
1. request : The request object represents httprequest that are trigged by service( )
invocation.
2. response : The response object represents the servers response to request.
3. pageContext : The page context specifies the single entry point to many of the page
attributes and is the convient place to put shared data.
4. session : the session object represents the session created by the current user.
5. application : the application object represents servlet context , obtained from servlet
configaration .
6. out : the out object represents to write the out put stream .
7. Config :the config object represents the servlet config interface from this page,and has
scope attribute.
8. page : The object is th eInstance of page implementation servlet class that are
processing the current request.
9. exception : These are used for different purposes and actually u no need to create
these objects in JSP. JSP container will create these objects automatically.
You can directly use these objects.
Example:
If i want to put my username in the session in JSP.
JSP Page: In the about page, i am using session object. But this session object is not
declared in JSP file, because, this is implicit object and it will be created by the jsp
container.
If u see the java file for this jsp page in the work folder of apache tomcat, u will find these
objects are created.
What is jsp:usebean. What are the scope attributes & difference between these
attributes
page, request, session, application
What is difference between scriptlet and expression
With expressions in JSP, the results of evaluating the expression are converted to a
string and directly included within the output page. Typically expressions are used to
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JAVA & J2EE
display simple values of variables or return values by invoking a bean's getter methods. JSP
expressions begin within tags and do not include semicolons:
But scriptlet can contain any number of language statements, variable or method
declarations, or expressions that are valid in the page scripting language. Within scriptlet
tags, you can declare variables or methods to use later in the file, write expressions valid in
the page scripting language,use any of the JSP mplicit objects or any object declared with a
What is Declaration
Declaration is used in JSP to declare methods and variables.To add a declaration, you
must use the sequences to enclose your declarations.
How do you connect to the database from JSP
To be precise to connect jdbc from jsp is not good idea ofcourse if ur working on
dummy projects connecting to msaccess u can very well use the same connection objects
amd methods in ur scriplets and define ur connection object in init() method.
But if its real time u can use DAO design patterns which is widely used. for ex u write
all ur connection object and and sql quires in a defiened method later use transfer object
[TO ]which is all ur fields have get/set methods and call it in business object[BO] so DAO is
accessd with precaution as it is the crucial. Finally u define java bean which is a class
holding get/set method implementing serialization thus the bean is called in the jsp. So
never connect to jdbc directly from client side since it can be hacked by any one to get ur
password or credit card info.
How do you call stored procedures from JSP
By using callable statement we can call stored procedures and functions from the database.
How do you restrict page errors display in the JSP page
set isErrorPage=false
How do you pass control from one JSP page to another
we can forward control to aother jsp using jsp action tags forward or incllude
How do I have the JSP-generated servlet subclass my own custom servlet class,
instead of the default?
One should be very careful when having JSP pages extend custom servlet classes as
opposed to the default one generated by the JSP engine. In doing so, you may lose out on
any advanced optimization that may be provided by the JSPengine. In any case, your new
superclass has to fulfill the contract with the JSPngine by: Implementing the HttpJspPage
interface, if the protocol used is HTTP, or implementing JspPage otherwise Ensuring that all
the methods in the Servlet interface are declared final Additionally, your servlet superclass
also needs to do the following:
The service() method has to invoke the _jspService() method
The init() method has to invoke the jspInit() method
The destroy() method has to invoke jspDestroy()
If any of the above conditions are not satisfied, the JSP engine may throw a translation
error. Once the superclass has been developed, you can have your JSP extend it as follows:
<%@ page extends="packageName.ServletName" %<
How does a servlet communicate with a JSP page?
The following code snippet shows how a servlet instantiates a bean and initializes it with
FORM data posted by a browser. The bean is then placed into the request, and the call is
then forwarded to the JSP page, Bean1.jsp, by means of a request dispatcher for
downstream processing.
public void doPost (HttpServletRequest request, HttpServletResponse response)
{
try {
govi.FormBean f = new govi.FormBean();
String id = request.getParameter("id");
f.setName(request.getParameter("name"));
f.setAddr(request.getParameter("addr"));
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JAVA & J2EE
f.setAge(request.getParameter("age"));
//use the id to compute
//additional bean properties like info
//maybe perform a db query, etc.
// . . .
f.setPersonalizationInfo(info);
request.setAttribute("fBean",f);
getServletConfig().getServletContext().getRequestDispatcher
("/jsp/Bean1.jsp").forward(request, response);
} catch (Exception ex) {
. . .
} }
The JSP page Bean1.jsp can then process fBean, after first extracting it from the default
request scope via the useBean action.
jsp:useBean id="fBean" class="govi.FormBean" scope="request"/
jsp:getProperty name="fBean" property="name" /
jsp:getProperty name="fBean" property="addr" /
jsp:getProperty name="fBean" property="age" /
jsp:getProperty name="fBean" property="personalizationInfo" /
Is there a way I can set the inactivity lease period on a per-session basis?
Typically, a default inactivity lease period for all sessions is set within your JSPengine
admin screen or associated properties file. However, if your JSP engine supports the Servlet
2.1 API, you can manage the inactivity lease period on a per-session basis. This is done by
invoking the HttpSession.setMaxInactiveInterval() method, right after the session has been
created.
For example:
<% session.setMaxInactiveInterval(300); %>
would reset the inactivity period for this session to 5 minutes. The inactivity interval is set
in seconds.
How can I set a cookie and delete a cookie from within a JSP page?
A cookie, mycookie, can be deleted using the following scriptlet:
<%
//creating a cookie
Cookie mycookie = new Cookie("aName","aValue");
response.addCookie(mycookie);
//delete a cookie
Cookie killMyCookie = new Cookie("mycookie", null);
killMyCookie.setMaxAge(0);
killMyCookie.setPath("/");
response.addCookie(killMyCookie);
%>
How can I declare methods within my JSP page?
You can declare methods for use within your JSP page as declarations. The methods can
then be invoked within any other methods you declare, or within JSP scriptlets and
expressions.
Do note that you do not have direct access to any of the JSP implicit objects like request,
response, session and so forth from within JSP methods. However, you should be able to
pass any of the implicit JSP variables as parameters to the methods you declare.
For example:
<%!
public String whereFrom(HttpServletRequest req) {
HttpSession ses = req.getSession();
...
return req.getRemoteHost();
}
%>
<%
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JAVA & J2EE
out.print("Hi there, I see that you are coming in from ");
%>
<%= whereFrom(request) %>
Another Example:
file1.jsp:
<%@page contentType="text/html"%>
<%!
public void test(JspWriter writer) throws IOException{
writer.println("Hello!");
}
%>
file2.jsp
<%@include file="file1.jsp"%>
<html>
<body>
<%test(out);% >
</body>
</html>
How can I enable session tracking for JSP pages if the browser has disabled
cookies?
We know that session tracking uses cookies by default to associate a session
identifier with a unique user. If the browser does not support cookies, or if cookies are
disabled, you can still enable session tracking using URL rewriting. URL rewriting essentially
includes the session ID within the link itself as a name/value pair. However, for this to be
effective, you need to append the session ID for each and every link that is part of your
servlet response. Adding the session ID to a link is greatly simplified by means of of a
couple of methods: response.encodeURL() associates a session ID with a given URL, and if
you are using redirection, response.encodeRedirectURL() can be used by giving the
redirected URL as input. Both encodeURL() and encodeRedirectedURL() first determine
whether cookies are supported by the browser; if so, the input URL is returned unchanged
since the session ID will be persisted as a cookie.
Consider the following example, in which two JSP files, say hello1.jsp and hello2.jsp,
interact with each other. Basically, we create a new session within hello1.jsp and place an
object within this session. The user can then traverse to hello2.jsp by clicking on the link
present within the page.Within hello2.jsp, we simply extract the object that was earlier
placed in the session and display its contents. Notice that we invoke the encodeURL() within
hello1.jsp on the link used to invoke hello2.jsp; if cookies are disabled, the session ID is
automatically appended to the URL, allowing hello2.jsp to still retrieve the session object.
Try this example first with cookies enabled. Then disable cookie support, restart the
brower, and try again. Each time you should see the maintenance of the session across
pages. Do note that to get this example to work with cookies disabled at the browser, your
JSP engine has to support URL rewriting.
hello1.jsp
<%@ page session="true" %>
<%
Integer num = new Integer(100);
session.putValue("num",num);
String url =response.encodeURL("hello2.jsp");
%>
<a href='<%=url%>'>hello2.jsp</a>
hello2.jsp
<%@ page session="true" %>
<%
Integer i= (Integer )session.getValue("num");
out.println("Num value in session is "+i.intValue());
How do I use a scriptlet to initialize a newly instantiated bean?
A jsp:useBean action may optionally have a body. If the body is specified, its contents will
be automatically invoked when the specified bean is instantiated. Typically, the body will
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JAVA & J2EE
contain scriptlets or jsp:setProperty tags to initialize the newly instantiated bean, although
you are not restricted to using those alone. The following example shows the "today"
property of the Foo bean initialized to the current date when it is instantiated. Note that
here, we make use of a JSP expression within the jsp:setProperty action.
<jsp:useBean id="foo" class="com.Bar.Foo" >
<jsp:setProperty name="foo" property="today"
value="<%=java.text.DateFormat.getDateInstance().format(new java.util.Date())
%>"/ >
<%-- scriptlets calling bean setter methods go here --%>
</jsp:useBean >
How does JSP handle run-time exceptions?
You can use the errorPage attribute of the page directive to have uncaught runtime
exceptions automatically forwarded to an error processing page.
For example:
<%@ page errorPage="error.jsp" %>
redirects the browser to the JSP page error.jsp if an uncaught exception is encountered
during request processing. Within error.jsp, if you indicate that it is an error-processing
page, via the directive:
<%@ page isErrorPage="true" %>
the Throwable object describing the exception may be accessed within the error page via
the exception implicit object.
Note: You must always use a relative URL as the value for the errorPage attribute.
How do I prevent the output of my JSP or Servlet pages from being cached by the
browser?
You will need to set the appropriate HTTP header attributes to prevent the dynamic
content output by the JSP page from being cached by the browser. Just execute the
following scriptlet at the beginning of your JSP pages to prevent them from being cached at
the browser. You need both the statements to take care of some of the older browser
versions.
<%
response.setHeader("Cache-Control","no-store"); //HTTP 1.1
response.setHeader("Pragma","no-cache"); //HTTP 1.0
response.setDateHeader ("Expires", 0); //prevents caching at the proxy server
%>
How do I use comments within a JSP page
You can use "JSP-style" comments to selectively block out code while debugging or
simply to comment your scriptlets. JSP comments are not visible at the client.
For example:
<%-- the scriptlet is now commented out
<%
out.println("Hello World");
%> --%>
You can also use HTML-style comments anywhere within your JSP page. These comments
are visible at the client. For example:

Of course, you can also use comments supported by your JSP scripting language within
your scriptlets. For example, assuming Java is the scripting language, you can have:
<%
//some comment
/**
yet another comment **/ %>
Can I stop JSP execution while in the midst of processing a request?
Yes. Preemptive termination of request processing on an error condition is a good way
to maximize the throughput of a high-volume JSP engine. The trick (asuming Java is your
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JAVA & J2EE
scripting language) is to use the return statement when you want to terminate further
processing. For example, consider:
<% if (request.getParameter("foo") != null) {
// generate some html or update bean property
} else {
/* output some error message or provide redirection back to the input form after creating a
memento bean updated with the 'valid' form elements that were input. This bean can now
be used by the previous form to initialize the input elements that were valid then, return
from the body of the _jspService() method to terminate further processing */
return;
}
%>
Is there a way to reference the "this" variable within a JSP page?
Yes, there is. Under JSP 1.0, the page implicit object is equivalent to "this", and returns
a reference to the servlet generated by the JSP page.
How do I perform browser redirection from a JSP page?
You can use the response implicit object to redirect the browser to a different resource, as:
response.sendRedirect("http://www.exforsys.com/path/error.html");
You can also physically alter the Location HTTP header attribute, as shown below:
<%
response.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
String newLocn = "/newpath/index.html";
response.setHeader("Location",newLocn);
%>
You can also use the: <jsp:forward page="/newpage.jsp" /> Also note that you can only
use this before any output has been sent to the client. I beleve this is the case with the
response.sendRedirect() method as well. If you want to pass any paramateres then you can
pass using
<jsp:forward page="/servlet/login"> <jsp:param name="username"
value="HARI" /> </jsp:forward>
How do I include static files within a JSP page?
Answer Static resources should always be included using the JSP include directive. This
way, the inclusion is performed just once during the translation phase. The following
example shows the syntax:
<%@ include file="copyright.html" %>
Do note that you should always supply a relative URL for the file attribute. Although you
can also include static resources using the action, this is not advisable as the inclusion is
then performed for each and every request.
What JSP lifecycle methods can I override?
You cannot override the _jspService() method within a JSP page. You can however,
override the jspInit() and jspDestroy() methods within a JSP page. jspInit() can be useful
for allocating resources like database connections, network connections, and so forth for
the JSP page. It is good programming practice to free any allocated resources within
jspDestroy().
The jspInit() and jspDestroy() methods are each executed just once during the lifecycle of a
JSP page and are typically declared as JSP declarations:
<%! public void jspInit() {
. . . }
%>
<%!
public void jspDestroy() {
. . . }
%>
Can a JSP page process HTML FORM data?
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JAVA & J2EE
Yes. However, unlike servlets, you are not required to implement HTTP-protocol specific
methods like doGet() or doPost() within your JSP page. You can obtain the data for the
FORM input elements via the request implicit object within a scriptlet or expression as:
<%
String item = request.getParameter("item");
int howMany = new Integer(request.getParameter("units")).intValue();
%>
or
<%= request.getParameter("item") %>
How do I mix JSP and SSI #include?
If you're just including raw HTML, use the #include directive as usual inside your .jsp file.

But it's a little trickier if you want the server to evaluate any JSP code that's inside the
included file. If your data.inc file contains jsp code you will have to use <%@
vinclude="data.inc" %> The  is used for including non-JSP
files.
How can I implement a thread-safe JSP page?
You can make your JSPs thread-safe by having them implement the SingleThreadModel
interface. This is done by adding the directive
<%@ page isThreadSafe="false" % > within your JSP page.
How do I include static files within a JSP page?
Static resources should always be included using the JSP include directive. This way, the
inclusion is performed just once during the translation phase. The following example shows
the syntax: Do note that you should always supply a relative URL for the file attribute.
Although you can also include static resources using the action, this is not advisable as the
inclusion is then performed for each and every request.
How do you prevent the Creation of a Session in a JSP Page and why?
By default, a JSP page will automatically create a session for the request if one does not
exist. However, sessions consume resources and if it is not necessary to maintain a session,
one should not be created. For example, a marketing campaign may suggest the reader
visit a web page for more information. If it is anticipated that a lot of traffic will hit that
page, you may want to optimize the load on the machine by not creating useless sessions.
What is the page directive is used to prevent a JSP page from automatically
creating a session:
<%@ page session="false">
Is it possible to share an HttpSession between a JSP and EJB? What happens
when I change a value in the HttpSession from inside an EJB?
You can pass the HttpSession as parameter to an EJB method, only if all objects in
session are serializable.This has to be consider as "passed-by-value", that means that it's
read-only in the EJB. If anything is altered from inside the EJB, it won't be reflected back to
the HttpSession of the Servlet Container.The "pass-byreference" can be used between EJBs
Remote Interfaces, as they are remote references. While it IS possible to pass an
HttpSession as a parameter to an EJB object, it is considered to be "bad practice (1)" in
terms of object oriented design. This is because you are creating an unnecessary coupling
between back-end objects (ejbs) and front-end objects (HttpSession). Create a higher-level
of abstraction for your ejb's api. Rather than passing the whole, fat, HttpSession (which
carries with it a bunch of http semantics), create a class that acts as a value object (or
structure) that holds all the data you need to pass back and forth between front-end/back-
end. Consider the case where your ejb needs to support a non-http-based client. This
higher level of abstraction will be flexible enough to support it. (1) Core J2EE design
patterns (2001)
Can a JSP page instantiate a serialized bean?
45

JAVA & J2EE
No problem! The useBean action specifies the beanName attribute, which can be used
for indicating a serialized bean. For example:
<jsp:useBean id="shop" type="shopping.CD" beanName="CD" />
<jsp:getProperty name="shop" property="album" />
A couple of important points to note. Although you would have to name your serialized file
"filename.ser", you only indicate "filename" as the value for the beanName attribute. Also,
you will have to place your serialized file within the WEB-INFjspbeans directory for it to be
located by the JSP engine.
Can you make use of a ServletOutputStream object from within a JSP page?
No. You are supposed to make use of only a JSPWriter object (given to you in the form of
the implicit object out) for replying to clients. A JSPWriter can be viewed as a buffered
version of the stream object returned by response.getWriter(), although from an
implementational perspective, it is not. A page author can always disable the default
buffering for any page using a page directive as:
<%@ page buffer="none" %>
Can we implements interface or extends class in JSP?
No , we can't implements interface or extends class in JSP
What are the steps required in adding a JSP Tag Libraries?
1. Create a TLD file and configure the required class Information.
2. Create the Java Implementation Source extending the JSP Tag Lib Class (TagSupport).
3. Compile and package it as loosed class file or as a jar under lib folder in Web Archive File
for Class loading.
4. Place the TLD file under the WEB-INF folder.
5. Add reference to the tag library in the web.xml file.
Struts 1.1
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JAVA & J2EE
1. Introduction to MVC
a. Overview of MVC Architecture
b. Applying MVC in Servlets and JSP
c. View on JSP
d. JSP Model 1 Architecture
e. JSP Model 2 Architecture
f. Limitation in traditional MVC approach
g. MVC Model 2 Architecture
h. The benefits
i. Application flow
2. Overview of Struts Framework
a. Introduction to Struts Framework
b. Struts Architecture
c. Front Controller Design Pattern
d. Controller servlet - ActionServlet
e. Action objects
f. Action Form objects
g. Action mappings
h. Configuring web.xml file and struts-config.xml file
3. Struts – View components
a. Composite View
b. Building page from templates
c. Jsp:include Vs struts template mechanism
d. Bean tags
e. Html tags
f. Logic tags
g. Template tags
4. Struts – Controller components
a. Action classes
b. ActionServlet
c. Struts data source
5. Advanced Struts
a. Accessing Application Resource File
b. Use of Tokens
c. Accessing Indexed properties
d. Forward Vs Redirect
e. Dynamic creating Action Forwards
6. Struts 1.1
a. DynaActionForm
b. DynaValidatorActionForm
Validating Input Data
Declarative approach
Using Struts Validator
Configuring the Validator
Specifying validation rules
Client side validation
c. Plugins
d. I18N (InternationalizatioN)
Specifying a resource bundle
Generating Locale specific messages
e. Tiles
Introduction to MVC(Model View Controler)
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JAVA & J2EE
Struts : Struts is an open source framework from Jakartha Project designed for developing
the web applications with Java SERVLET API and Java Server Pages Technologies.Struts
conforms the Model View Controller design pattern. Struts package provides unified
reusable components (such as action servlet) to build the user interface that can be applied
to any web connection. It encourages software development following the MVC design
pattern.
Overview of MVC Architecture
The MVC design pattern divides applications into three components:
• The Model maintains the state and data that the application represents .
• The View allows the display of information about the model to the user.
• The Controller allows the user to manipulate the application .
In Struts, the view is handled by JSPs and presentation components, the model is
represented by Java Beans and the controller uses Servlets to perform its action.
By developing a familiar Web-based shopping cart, you'll learn how to utilize the Model-
View-Controller (MVC) design pattern and truly separate presentation from content when
using Java Server Pages.
Applying MVC in Servlets and JSP
Many web applications are JSP-only or Servlets-only. With JSP, Java code is
embedded in the HTML code; with Servlets the Java code calls println methods to generate
the HTML code. Both approaches have their advantages and drawbacks; Struts gathers
their strengths to get the best of their association.
Below you will find one example on registration form processing using MVC in Servlets and
JSP:
48
Controller Servlet
Users

UI Components
UI Process Components
Service Interfaces
Business
Workflows
Business
Components
Business
Entities
Data Access Logic
Components
Service Agents
Data Sources

Services

Secur
i
t
y
Opera
t
i
ona
lmanagement
Commun
i
ca
t
i
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JAVA & J2EE
1. In the above application Reg.jsp act as view accepts I/P from client and submits to
Controller Servlet.
2. Controller Servlet validates the form data, if valid, stores the data into DB
3. Based on the validation and DB operations Controller Servlet decides to respond
either Confirm.jsp or Error.jsp to client’s browser.
4. When the Error.jsp is responded, the page must include all the list of errors with
detailed description.
5. The above shown application architecture is the model for MVC.
6. IF MVC Model 2 wants to be implemented in your application business logic and
model operations must be separated from controller program.
View on JSP
The early JSP specification follows two approaches for building applications using
JSP technology. These two approaches are called as JSP Model 1 and JSP Model 2
architectures.
JSP Model 1 Architecture
In Model 1 architecture the JSP page is alone responsible for processing the
incoming request and replying back to the client. There is still separation of presentation
from content, because all data access is performed using beans. Although the JSP Model 1
Architecture is more suitable for simple applications, it may not be desirable for complex
implementations.
JSP Model 2 Architecture
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The Model 2 Architecture is an approach for serving dynamic content, since it
combines the use of both Servlets and JSP. It takes advantages of the predominant
strengths of both technologies, using JSP to generate the presentation layer and Servlets to
perform process-intensive tasks. Here servlet acts as controller and is in charge of request
processing and the creation of any beans or objects used by the JSP as well as deciding
depending on the user’s actions, which JSP page to forward the request to. Note that there
is no processing logic within the JSP page itself; it is simply responsible for retrieving any
objects or beans that may have been previously created by the servlet, and extracting the
dynamic content from that servlet for insertion within static templates.
Limitation in traditional MVC approach
The main limitation in the traditional MVC approach is, in that there is no separation
of business logic (validation/ conditions/ anything related to business rules) from controller
(is responsible for controlling of the application flow by using static/dynamic request
dispatcher.
MVC Model 2 Architecture is Model View Controller
1. Client submits login request to servlet application
2. Servlet application acts as controller it first decides to request validator another
servlet program which is responsible for not null checking (business rule)
3. control comes to controller back and based on the validation response, if the
response is positive, servlet controller sends the request to model
4. Model requests DB to verify whether the database is having the same user name
and password, If found login operation is successful
5. Beans are used to store if any data retrieved from the database and kept into
HTTPSession
6. Controller then gives response back to response JSP (view) which uses the bean
objects stored in HTTPSession object
7. and prepares presentation response on to the browser
Overview of Struts Framework
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Introduction to Struts Framework
The goal of this project is to provide an open source framework for building Java web
applications. The core of the Struts framework is a flexible control layer based on standard
technologies like Java Servlets, JavaBeans, Resource Bundles, and XML, as well as various
Jakarta Commons packages. Struts encourages application architectures based on the
Model 2 approach, a variation of the classic Model-View-Controller (MVC) design
paradigm.
Struts provides its own Controller component and integrates with other technologies to
provide the Model and the View.
• For the Model, Struts can interact with standard data access technologies, like JDBC and
EJB, as well as most any third-party packages, like Hibernate, iBATIS, or Object
Relational Bridge.
• For the View, Struts works well with Java Server Pages, including JSTL and JSF, as well
as Velocity Templates, XSLT, and other presentation systems.
• For Controller, ActionServlet and ActionMapping - The Controller portion of the
application is focused on receiving requests from the client deciding what business logic
function is to be performed, and then delegating responsibility for producing the next
phase of the user interface to an appropriate View component. In Struts, the primary
component of the Controller is a servlet of class ActionServlet. This servlet is configured
by defining a set of ActionMappings. An ActionMapping defines a path that is matched
against the request URI of the incoming request, and usually specifies the fully qualified
class name of an Action class. Actions encapsulate the business logic, interpret the
outcome, and ultimately dispatch control to the appropriate View component to create
the response.
The Struts project was launched in May 2000 by Craig McClanahan to provide a standard
MVC framework to the Java community. In July 2001.
In the MVC design pattern, application flow is mediated by a central Controller. The
Controller delegates’ requests - in our case, HTTP requests - to an appropriate handler. The
handlers are tied to a Model, and each handler acts as an adapter between the request and
the Model. The Model represents, or encapsulates, an application's business logic or state.
Control is usually then forwarded back through the Controller to the appropriate View. The
forwarding can be determined by consulting a set of mappings, usually loaded from a
database or configuration file. This provides a loose coupling between the View and Model,
which can make applications significantly easier to create and maintain.
Struts Architecture
Front Controller
Context
The presentation-tier request handling mechanism must control and coordinate
processing of each user across multiple requests. Such control mechanisms may be
managed in either a centralized or decentralized manner.
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Problem
The system requires a centralized access point for presentation-tier request handling to
support the integration of system services, content retrieval, view management, and
navigation. When the user accesses the view directly without going through a centralized
mechanism,
Two problems may occur:
 Each view is required to provide its own system services, often resulting in duplicate
code.
 View navigation is left to the views. This may result in commingled view content and
view navigation.
Additionally, distributed control is more difficult to maintain, since changes will often need
to be made in numerous places.
Solution :
Use a controller as the initial point of contact for handling a request. The controller
manages the handling of the request, including invoking security services such as
authentication and authorization, delegating business processing, managing the choice of
an appropriate view, handling errors, and managing the selection of content creation
strategies.
The controller provides a centralized entry point that controls and manages Web
request handling. By centralizing decision points and controls, the controller also helps
reduce the amount of Java code, called scriptlets, embedded in the JavaServer Pages (JSP)
page.
Centralizing control in the controller and reducing business logic in the view promotes
code reuse across requests. It is a preferable approach to the alternative-embedding code
in multiple views-because that approach may lead to a more error-prone, reuse-by-copy-
and-paste environment.
Typically, a controller coordinates with a dispatcher component. Dispatchers are
responsible for view management and navigation. Thus, a dispatcher chooses the next view
for the user and vectors control to the resource. Dispatchers may be encapsulated within
the controller directly or can be extracted into a separate component.
While the Front Controller pattern suggests centralizing the handling of all
requests, it does not limit the number of handlers in the system, as does a Singleton. An
application may use multiple controllers in a system, each mapping to a set of distinct
services.
Structure
Below figure represents the Front Controller class diagram pattern.
Figure: Front Controller class diagram
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Participants and Responsibilities
Below figure shows the sequence diagram representing the Front Controller pattern. It
depicts how the controller handles a request.
Figure: Front Controller sequence diagram
Controller : The controller is the initial contact point for handling all requests in the
system. The controller may delegate to a helper to complete authentication and
authorization of a user or to initiate contact retrieval.
Dispatcher :
A dispatcher is responsible for view management and navigation, managing the
choice of the next view to present to the user, and providing the mechanism for vectoring
control to this resource.
A dispatcher can be encapsulated within a controller or can be a separate component
working in coordination. The dispatcher provides either a static dispatching to the view or a
more sophisticated dynamic dispatching mechanism.
The dispatcher uses the Request Dispatcher object (supported in the servlet
specification) and encapsulates some additional processing.
Helper :
A helper is responsible for helping a view or controller complete its processing. Thus,
helpers have numerous responsibilities, including gathering data required by the view and
storing this intermediate model, in which case the helper is sometimes referred to as a
value bean. Additionally, helpers may adapt this data model for use by the view. Helpers
can service requests for data from the view by simply providing access to the raw data or
by formatting the data as Web content.
A view may work with any number of helpers, which are typically implemented as
JavaBeans components (JSP 1.0+) and custom tags (JSP 1.1+). Additionally, a helper may
represent a Command object, a delegate, or an XSL Transformer, which is used in
combination with a stylesheet to adapt and convert the model into the appropriate form.
View : A view represents and displays information to the client. The view retrieves
information from a model. Helpers support views by encapsulating and adapting the
underlying data model for use in the display.
Action Form class
An ActionForm represents an HTML form that the user interacts with over one or more
pages. You will provide properties to hold the state of the form with getters and setters to
access them. ActionForms can be stored in either the session (default) or request scopes. If
they're in the session it's important to implement the form's reset method to initialize the
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form before each use. Struts sets the ActionForm's properties from the request parameters
and sends the validated form to the appropriate Action's execute method.
When you code your ActionForm beans, keep the following principles in mind:
• The ActionForm class itself requires no specific methods to be implemented. It is
used to identify the role these particular beans play in the overall architecture.
Typically, an ActionForm bean will have only property getter and property setter
methods, with no business logic.
• The ActionForm object also offers a standard validation mechanism. If you override
a "stub" method, and provide error messages in the standard application resource,
Struts will automatically validate the input from the form (using your method). See
"Automatic Form Validation" for details. Of course, you can also ignore the
ActionForm validation and provide your own in the Action object.
• Define a property (with associated getXxx and setXxx methods) for each field that is
present in the form. The field name and property name must match according to the
usual JavaBeans conventions (see the Javadoc for the java.beans.Introspector class
for a start on information about this). For example, an input field named username
will cause the setUsername method to be called.
• Buttons and other controls on your form can also be defined as properties. This can
help determine which button or control was selected when the form was submitted.
Remember, the ActionForm is meant to represent your data-entry form, not just the
data beans.
• Think of your ActionForm beans as a firewall between HTTP and the Action. Use the
validate method to ensure all required properties are present, and that they contain
reasonable values. An ActionForm that fails validation will not even be presented to
the Action for handling.
• You may also place a bean instance on your form, and use nested property
references. For example, you might have a "customer" bean on your ActionForm,
and then refer to the property "customer.name" in your presentation page. This
would correspond to the methods customer.getName() and
customer.setName(string Name) on your customer bean. See the Tag Library
Developer Guides for more about using nested syntax with the Struts JSP tags.
• Caution: If you nest an existing bean instance on your form, think about the
properties it exposes. Any public property on an ActionForm that accepts a single
String value can be set with a query string. It may be useful to place beans that can
affect the business state inside a thin "wrapper" that exposes only the properties
required. This wrapper can also provide a filter to be sure runtime properties are not
set to inappropriate values.
Action class Design guidelines
Remember the following design guidelines when coding Action classes:
• Write code for a multi-threaded environment - The controller servlet creates only
one instance of your Action class, and uses this one instance to service all requests.
Thus, you need to write thread-safe Action classes. Follow the same guidelines you would
use to write thread-safe Servlets. Here are two general guidelines that will help you write
scalable, thread-safe Action classes:
o Only Use Local Variables - The most important principle that aids in thread-safe coding
is to use only local variables, not instance variables, in your Action class. Local
variables are created on a stack that is assigned (by your JVM) to each request thread, so
there is no need to worry about sharing them. An Action can be factored into several local
methods, so long as all variables needed are passed as method parameters. This assures
thread safety, as the JVM handles such variables internally using the call stack which is
associated with a single Thread.
o Conserve Resources - As a general rule, allocating scarce resources and keeping them
across requests from the same user (in the user's session) can cause scalability problems.
For example, if your application uses JDBC and you allocate a separate JDBC connection
for every user, you are probably going to run in some scalability issues when your site
suddenly shows up on Slashdot. You should strive to use pools and release resources (such
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as database connections) prior to forwarding control to the appropriate View component --
even if a bean method you have called throws an exception.
Action mapping implementation
In order to operate successfully, the Struts controller servlet needs to know several things
about how each request URI should be mapped to an appropriate Action class. The required
knowledge has been encapsulated in a Java class named ActionMapping, the most
important properties are as follows:
o type - Fully qualified Java class name of the Action implementation class used by this
mapping.
o name - The name of the form bean defined in the config file that this action will use.
o path - The request URI path that is matched to select this mapping. See below for
examples of how matching works and how to use wildcards to match multiple request
URIs.
o unknown - Set to true if this action should be configured as the default for this application,
to handle all requests not handled by another action. Only one action can be defined as a
default within a single application.
o validate - Set to true if the validate method of the action associated with this mapping
should be called.
o forward - The request URI path to which control is passed when this mapping is invoked.
This is an alternative to declaring a type property.
Writing Action Mappings
How does the controller servlet learn about the mappings you want? It would be possible
(but tedious) to write a small Java class that simply instantiated new ActionMapping
instances, and called all of the appropriate setter methods. To make this process easier,
Struts uses the Jakarta Commons Digester component to parse an XML-based description
of the desired mappings and create the appropriate objects initialized to the appropriate
default values. See the Jakarta Commons website for more information about the Digester.
The developer's responsibility is to create an XML file named struts-config.xml and place it
in the WEB-INF directory of your application. This format of this document is described by
the Document Type Definition (DTD) maintained at
http://jakarta.apache.org/struts/dtds/struts-config_1_2.dtd. This chapter covers the
configuration elements that you will typically write as part of developing your application.
There are several other elements that can be placed in the struts-config file to customize
your application. See "Configuring Applications" for more about the other elements in the
Struts configuration file.
The controller uses an internal copy of this document to parse the configuration; an
Internet connection is not required for operation.
The outermost XML element must be <struts-config>. Inside of the <struts-config>
element, there are three important elements that are used to describe your actions:
• <form-beans>
• <global-forwards>
• <action-mappings>
<form-beans>
This section contains your form bean definitions. Form beans are descriptors that are used
to create ActionForm instances at runtime. You use a <form-bean> element for each form
bean, which has the following important attributes:
• name: A unique identifier for this bean, which will be used to reference it in
corresponding action mappings. Usually, this is also the name of the request or
session attribute under which this form bean will be stored.
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• type: The fully-qualified Java classname of the ActionForm subclass to use with this
form bean.
<global-forwards>
This section contains your global forward definitions. Forwards are instances of the
ActionForward class returned from an ActionForm's execute method. These map logical
names to specific resources (typically JSPs), allowing you to change the resource without
changing references to it throughout your application. You use a <forward> element for
each forward definition, which has the following important attributes:
• name: The logical name for this forward. This is used in your ActionForm's execute
method to forward to the next appropriate resource. Example: homepage
• path: The context relative path to the resource. Example: /index.jsp or /index.do
• redirect: True or false (default). Should the ActionServlet redirect to the resource
instead of forward?
<action-mappings>
This section contains your action definitions. You use an <action> element for each of the
mappings you would like to define. Most action elements will define at least the following
attributes:
• path: The application context-relative path to the action.
• type: The fully qualified java classname of your Action class.
• name: The name of your <form-bean> element to use with this action
Other often-used attributes include:
• parameter: A general-purpose attribute often used by "standard" Actions to pass a
required property.
• roles: A comma-delimited list of the user security roles that can access this
mapping.
For a complete description of the elements that can be used with the action element, see
the Struts Configuration DTD and the ActionMapping documentation.
Action Mapping Example
Here's a mapping entry based on the MailReader example application. The MailReader
application now uses DynaActionForms. But in this example, we'll show a conventinal
ActionForm instead, to illustrate the usual workflow. Note that the entries for all the other
actions are left out:
<struts-config>
<form-beans>
<form-bean
name="logonForm"
type="org.apache.struts.webapp.example.LogonForm" />
</form-beans>
<global-forwards
type="org.apache.struts.action.ActionForward">
<forward
name="logon"
path="/logon.jsp"
redirect="false" />
</global-forwards>
<action-mappings>
<action
path ="/logon"
type ="org.apache.struts.webapp.example.LogonAction"
name ="logonForm"
scope ="request"
input ="/logon.jsp"
unknown="false"
validate="true" />
</action-mappings>
</struts-config>
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First the form bean is defined. A basic bean of class
"org.apache.struts.webapp.example.LogonForm" is mapped to the logical name
"logonForm". This name is used as a request attribute name for the form bean.
The "global-forwards" section is used to create logical name mappings for commonly
used presentation pages. Each of these forwards is available through a call to your action
mapping instance, i.e. mapping.findForward("logicalName").
As you can see, this mapping matches the path /logon (actually, because the
MailReader example application uses extension mapping, the request URI you specify in a
JSP page would end in /logon.do). When a request that matches this path is received, an
instance of the LogonAction class will be created (the first time only) and used. The
controller servlet will look for a bean in request scope under key logonForm, creating and
saving a bean of the specified class if needed.
Optional but very useful are the local "forward" elements. In the MailReader example
application, many actions include a local "success" and/or "failure" forward as part of an
action mapping.

<action
path="/editSubscription"
type="org.apache.struts.webapp.example.EditSubscriptionAction"
name="subscriptionForm"
scope="request"
validate="false">
<forward
name="failure"
path="/mainMenu.jsp"/>
<forward
name="success"
path="/subscription.jsp"/>
</action>
Using just these two extra properties, the Action classes are almost totally independent
of the actual names of the presentation pages. The pages can be renamed (for example)
during a redesign, with negligible impact on the Action classes themselves. If the names of
the "next" pages were hard coded into the Action classes, all of these classes would also
need to be modified. Of course, you can define whatever local forward properties makes
sense for your own application.
The Struts configuration file includes several other elements that you can use to customize
your application. See "Configuring Applications" for details.
Using Action Mapping for pages
Fronting your pages with ActionMappings is essential when using modules, since doing so is
the only way you involve the controller in the request -- and you want to! The controller
puts the application configuration in the request, which makes available all of your module-
specific configuration data (including which message resources you are using, request-
processor, datasources, and so forth).
The simplest way to do this is to use the forward property of the ActionMapping:
<action path="/view" forward="/view.jsp"/>
Configuring struts-config.xml file
The Building Controller Components chapter covered writing the form-bean and
action-mapping portions of the Struts configuration file. These elements usually play an
important role in the development of a Struts application. The other elements in Struts
configuration file tend to be static: you set them once and leave them alone.
These "static" configuration elements are:
• controller
• message-resources
• plug-in
• data-sources
Controller configuration
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The <controller> element allows you to configure the ActionServlet. Many of the
controller parameters were previously defined by servlet initialization parameters in your
web.xml file but have been moved to this section of struts-config.xml in order to allow
different modules in the same web application to be configured differently. For full details
on available parameters see the struts-config_1_2.dtd or the list below.
• bufferSize - The size (in bytes) of the input buffer used when processing file
uploads. [4096] (optional)
• className - Classname of configuration bean.
[org.apache.struts.config.ControllerConfig] (optional)
• contentType - Default content type (and optional character encoding) to be set on
each response. May be overridden by the Action, JSP, or other resource to which the
request is forwarded. [text/html] (optional)
• forwardPattern - Replacement pattern defining how the "path" attribute of a
<forward> element is mapped to a context-relative URL when it starts with a slash
(and when the contextRelative property is false). This value may consist of any
combination of the following:
o $M - Replaced by the module prefix of this module.
o $P - Replaced by the "path" attribute of the selected <forward> element.
o $$ - Causes a literal dollar sign to be rendered.
o $x - (Where "x" is any character not defined above) Silently swallowed,
reserved for future use.
If not specified, the default forwardPattern is consistent with the previous behavior
of forwards. [$M$P] (optional)
• inputForward - Set to true if you want the input attribute of <action> elements
to be the name of a local or global ActionForward, which will then be used to
calculate the ultimate URL. Set to false to treat the input parameter of <action>
elements as a module-relative path to the resource to be used as the input form.
[false] (optional)
• locale - Set to true if you want a Locale object stored in the user's session if not
already present. [true] (optional)
• maxFileSize - The maximum size (in bytes) of a file to be accepted as a file upload.
Can be expressed as a number followed by a "K", "M", or "G", which are interpreted
to mean kilobytes, megabytes, or gigabytes, respectively. [250M] (optional)
• multipartClass - The fully qualified Java class name of the multipart request
handler class to be used with this module.
[org.apache.struts.upload.CommonsMultipartRequestHandler] (optional)
• nocache - Set to true if you want the controller to add HTTP headers for defeating
caching to every response from this module. [false] (optional)
• pagePattern - Replacement pattern defining how the page attribute of custom tags
using it is mapped to a context-relative URL of the corresponding resource. This
value may consist of any combination of the following:
o $M - Replaced by the module prefix of this module.
o $P - Replaced by the "path" attribute of the selected <forward> element.
o $$ - Causes a literal dollar sign to be rendered.
o $x - (Where "x" is any character not defined above) Silently swallowed,
reserved for future use.
If not specified, the default pagePattern is consistent with the previous behavior of
URL calculation. [$M$P] (optional)
• processorClass - The fully qualified Java class name of the RequestProcessor
subclass to be used with this module. [org.apache.struts.action.RequestProcessor]
(optional)
• tempDir - Temporary working directory to use when processing file uploads. [{the
directory provided by the servlet container}]
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This example uses the default values for several controller parameters. If you only want
default behavior you can omit the controller section altogether.
<controller
processorClass="org.apache.struts.action.RequestProcessor"
debug="0"
contentType="text/html"/>;
...
</struts-config>
Finally, you could use org.apache.struts.actions.SwitchAction, like so:
...
<action-mappings>
<action path="/toModule"
type="org.apache.struts.actions.SwitchAction"/>
...
</action-mappings>
...
Now, to change to ModuleB, we would use a URI like this:
http://localhost:8080/toModule.do?prefix=/moduleB&page=/index.do
If you are using the "default" module as well as "named" modules (like "/moduleB"), you
can switch back to the "default" module with a URI like this:
http://localhost:8080/toModule.do?prefix=&page=/index.do
That's all there is to it! Happy module-switching!
The Web Application Deployment Descriptor
The final step in setting up the application is to configure the application deployment
descriptor (stored in file WEB-INF/web.xml) to include all the Struts components that are
required. Using the deployment descriptor for the example application as a guide, we see
that the following entries need to be created or modified.
Configure the Action Servlet Instance
• config/${module} - Context-relative path to the XML resource containing the
configuration information for the application module that will use the specified prefix (/$
{module}). This can be repeated as many times as required for multiple application
modules. (Since Struts 1.1)
• convertNull - Force simulation of the Struts 1.0 behavior when populating forms. If set to
true, the numeric Java wrapper class types (like java.lang.Integer) will default to null
(rather than 0). (Since Struts 1.1) [false]
• rulesets - Comma-delimited list of fully qualified classnames of additional
org.apache.commons.digester.RuleSet instances that should be added to the Digester
that will be processing struts-config.xml files. By default, only the RuleSet for the
standard configuration elements is loaded. (Since Struts 1.1)
• validating - Should we use a validating XML parser to process the configuration file
(strongly recommended)? [true]
WARNING - Struts will not operate correctly if you define more than one <servlet>
element for a controller servlet, or a subclass of the standard controller servlet class. The
controller servlet MUST be a web application wide singleton.
Configure the Action Servlet Mapping
Note: The material in this section is not specific to Struts. The configuration of servlet
mappings is defined in the Java Servlet Specification. This section describes the most
common means of configuring a Struts application.
There are two common approaches to defining the URLs that will be processed by the
controller servlet -- prefix matching and extension matching. An appropriate mapping entry
for each approach will be described below.
Prefix matching means that you want all URLs that start (after the context path part) with a
particular value to be passed to this servlet. Such an entry might look like this:
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>/do/*</url-pattern>
</servlet-mapping>
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which means that a request URI to match the /logon path described earlier might look like
this:
http://www.mycompany.com/myapplication/do/logon
where /myapplication is the context path under which your application is deployed.
Extension mapping, on the other hand, matches request URIs to the action servlet based on
the fact that the URI ends with a period followed by a defined set of characters. For
example, the JSP processing servlet is mapped to the *.jsp pattern so that it is called to
process every JSP page that is requested. To use the *.do extension (which implies "do
something"), the mapping entry would look like this:
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
and a request URI to match the /logon path described earlier might look like this:
http://www.mycompany.com/myapplication/logon.do
WARNING - Struts will not operate correctly if you define more than one <servlet-
mapping> element for the controller servlet.
WARNING - If you are using the new module support in Struts 1.1, you should be aware
that only extension mapping is supported.
Configure the Struts Tag Libraries
Next, you must add an entry defining the Struts tag library.
The struts-bean taglib contains tags useful in accessing beans and their properties, as well
as defining new beans (based on these accesses) that are accessible to the remainder of
the page via scripting variables and page scope attributes. Convenient mechanisms to
create new beans based on the value of request cookies, headers, and parameters are also
provided.
The struts-html taglib contains tags used to create struts input forms, as well as other tags
generally useful in the creation of HTML-based user interfaces.
The struts-logic taglib contains tags that are useful in managing conditional generation of
output text, looping over object collections for repetitive generation of output text, and
application flow management.
The struts-tiles taglib contains tags used for combining various view components, called
"tiles", into a final composite view.
The struts-nested taglib is an extension of other struts taglibs that allows the use of nested
beans.
Below is how you would define all taglibs for use within your application. In practice, you
would only specify the taglibs that your application uses:
<taglib>
<taglib-uri>/tags/struts-bean
This tells the JSP system where to find the tag library descriptor for this library (in your
application's WEB-INF directory, instead of out on the Internet somewhere).
Configure the Struts Tag Libraries (Servlet 2.3)
Servlet 2.3 Users only: The Servlet 2.3 specification simplifies the deployment and
configuration of tag libraries. The instructions above will work on older containers as well as
2.3 containers (Struts only requires a servlet 2.2 container); however, if you're using a 2.3
container such as Tomcat 4.x, you can take advantage of a simplified deployment.
All that's required to install the struts tag libraries is to copy struts.jar into your /WEB-
INF/lib directory and reference the tags in your code like this:
<%@ taglib uri=http://struts.apache.org/tags-html prefix="html" %>
Note that you must use the full uri defined in the various struts tlds so that the
container knows where to find the tag's class files. You don't have to alter your web.xml file
or copy tlds into any application directories.
Add Struts Components To Your Application
To use Struts, you must copy the .tld files that you require into your WEB-INF directory,
and copy struts.jar (and all of the commons-*.jar files) into your WEB-INF/lib directory.
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Struts Bean Tags
This tag library contains tags useful in accessing beans and their properties, as well as
defining new beans (based on these accesses) that are accessible to the remainder of the
page via scripting variables and page scope attributes. Convenient mechanisms to create
new beans based on the value of request cookies, headers, and parameters are also
provided.
Many of the tags in this tag library will throw a JspException at runtime when they are
utilized incorrectly (such as when you specify an invalid combination of tag attributes). JSP
allows you to declare an "error page" in the <%@ page %> directive. If you wish to
process the actual exception that caused the problem, it is passed to the error page as a
request attribute under key org.apache.struts.action.EXCEPTION.
If you are viewing this page from within the Struts Documentation Application (or online at
http://struts.apache.org/), you can learn more about using these tags in the Bean Tags
Developer's Guide.
Tag Name Description
cookie Define a scripting variable based on the value(s) of the specified request cookie.
define Define a scripting variable based on the value(s) of the specified bean property.
header Load the response from a dynamic application request and make it available as a
bean
include Render an internationalized message string to the response.
message Expose a specified item from the page context as a bean.
page Define a scripting variable based on the value(s) of the specified request parameter.
parameter Load a web application resource and make it available as a bean.
resource Define a bean containing the number of elements in a Collection or Map.
size Expose a named Struts internal configuration object as a bean.
struts Render the value of the specified bean property to the current JspWriter.
Struts
The core of the Struts framework is a flexible control layer based on standard technologies
like Java Servlets, JavaBeans, ResourceBundles, and XML, as well as various Jakarta
Commons packages. Struts encourages application architectures based on the Model 2
approach, a variation of the classic Model-View-Controller (MVC) design paradigm.
Struts provides its own Controller component and integrates with other technologies
to provide the Model and the View. For the Model, Struts can interact with standard data
access technologies, like JDBC and EJB, as well as most any third-party packages, like
Hibernate, iBATIS, or Object Relational Bridge. For the View, Struts works well with
JavaServer Pages, including JSTL and JSF, as well as Velocity Templates, XSLT, and other
presentation systems.
The Struts framework provides the invisible underpinnings every professional web
application needs to survive. Struts helps you create an extensible development
environment for your application, based on published standards and proven design
patterns.
What is the difference between Struts 1.0 and Struts 1.1
The new features added to Struts 1.1 are 1. RequestProcessor class 2. Method perform()
replaced by execute() in Struts base Action Class 3. Changes to web.xml and struts-
config.xml 4.Declarative exception handling 5.Dynamic ActionForms 6.Plug-ins 7.Multiple
Application Modules 8.Nested Tags 9.The Struts Validator 10.Change to the ORO package
11.Change to Commons logging 12.Removal of Admin actions 13. Deprecation of the
GenericDataSource
Explain Struts navigation flow
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A client requests a path that matches the Action URI pattern. The container passes the
request to the ActionServlet. If this is a modular application, the ActionServlet selects the
appropriate module. The ActionServlet looks up the mapping for the path. If the mapping
specifies a form bean, the ActionServlet sees if there is one already or creates one. If a
form bean is in play, the ActionServlet resets and populates it from the HTTP request. If the
mapping has the validate property set to true, it calls validate on the form bean. If it fails,
the servlet forwards to the path specified by the input property and this control flow ends.
If the mapping specifies an Action type, it is reused if it already exists or instantiated.
The Action’s perform or execute method is called and passed the instantiated form
bean (or null). The Action may populate the form bean, call business objects, and do
whatever else is needed. The Action returns an ActionForward to the ActionServlet. If the
ActionForward is to another Action URI, we begin again; otherwise, it’s off to a display page
or some other resource. Most often, it is a JSP, in which case Jasper, or the equivalent (not
Struts), renders the page.
What is the difference between ActionForm and DynaActionForm
In struts 1.0, action form is used to populate the html tags in jsp using struts custom
tag.when the java code changes, the change in action class is needed. To avoid the chages
in struts 1.1 dyna action form is introduced.This can be used to develop using xml.The dyna
action form bloats up with the struts-config.xml based definetion.
What is DispatchAction
The DispatchAction class is used to group related actions into one class. DispatchAction
is an abstract class, so you must override it to use it. It extends the Action class.
It should be noted that you dont have to use the DispatchAction to group multiple actions
into one Action class.
You could just use a hidden field that you inspect to delegate to member() methods inside
of your action.
How to call ejb from Struts
use the Service Locator patter to look up the ejbs
Or You can use InitialContext and get the home interface.
What is the difference between ActionErrors and ActionMessages
The difference between the classes is zero -- all behavior in ActionErrors was pushed up
into ActionMessages and all behavior in ActionError was pushed up into ActionMessage. This
was done in the attempt to clearly signal that these classes can be used to pass any kind of
messages from the controller to the view -- errors being only one kind of message
How you will handle errors and exceptions using Struts
There are various ways to handle exception:
1) To handle errors server side validation can be used using ActionErrors classes can be
used.
2) The exceptions can be wrapped across different layers to show a user showable
exception.
3)using validators
How you will save the data across different pages for a particular client request
using Struts
Several ways. The similar to the ways session tracking is enabled. Using cookies, URL-
rewriting, SSLSession, and possibilty threw in the database.
What we will define in Struts-config.xml file. And explain their purpose
The main control file in the Struts framework is the struts-config.xml XML file, where
action mappings are specified. This file's structure is described by the struts-config DTD file,
which is defined at http://jakarta.apache.org/struts/. A copy of the DTD can be found on
the /docs/dtds subdirectory of the framework's installation root directory. The top-level
element is struts-config. Basically, it consists of the following elements:
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data-sources—A set of data-source elements, describing parameters needed to instantiate
JDBC 2.0 Standard Extension DataSource objects
form-beans—A set of form-bean elements that describe the form beans that this
application uses
global-forwards—A set of forward elements describing general available forward URIs
action-mappings—A set of action elements describing a request-to-action mapping
What is the purpose of tiles-def.xml file, resourcebundle.properties file,
validation.xml file
The Tiles Framework is an advanced version of that comes bundled with the Struts
Webapp framework. Its purpose is reduce the duplication between jsp pages as well as
make layouts flexible and easy to maintain. It integrates with Struts using the concept of
named views or definitions.
What is Action Class. What are the methods in Action class
Action class is request handler in Struts. we will extend the Action class and over ride the
execute() method in which we will specify the business logic to be performed.
Explain about token feature in Struts
Tokens are used to check for invalid path for by the uer:
1) if the user presses back button and submits the same page
2)or if the user refreshes the page which will result to the resubmit of the previous action
and might lead to unstabality..
to solve the abv probs we use tokens
1) in previous action type saveTokens(HttpServletreuest)
2) in current action check for duplication bu
if(!isValidToken())
What part of MVC does Struts represent
Bad question. Struts is a framework which supports the MVC pattern.
What are the core classes of struts?
The core classes of struts are ActionForm, Action, ActionMapping, ActionForward etc.
What are the Important Components of Struts?
1. Action Servlet
2. Action Classes
3. Action Form
4. Validator Framework
5. Message Resources
6. Struts Configuration XML Files
7. View components like JSP
What is Struts?
Struts is a web page development framework and an open source software that helps
developers build web applications quickly and easily. Struts combines Java Servlets, Java
Server Pages, custom tags, and message resources into a unified framework. It is a
cooperative, synergistic platform, suitable for development teams, independent developers,
and everyone between.
How is the MVC design pattern used in Struts framework?
In the MVC design pattern, application flow is mediated by a central Controller. The
Controller delegates requests to an appropriate handler. The handlers are tied to a Model,
and each handler acts as an adapter between the request and the Model. The Model
represents, or encapsulates, an application's business logic or state. Control is usually then
forwarded back through the Controller to the appropriate View. The forwarding can be
determined by consulting a set of mappings, usually loaded from a database or
configuration file. This provides a loose coupling between the View and Model, which can
make an application significantly easier to create and maintain.
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Controller--Servlet controller which supplied by Struts itself; View --- what you can see on
the screen, a JSP page and presentation components; Model --- System state and a
business logic JavaBeans.
Who makes the Struts?
Struts is hosted by the Apache Software Foundation(ASF) as part of its Jakarta project,
like Tomcat, Ant and Velocity.
Why it called Struts?
Because the designers want to remind us of the invisible underpinnings that hold up our
houses, buildings, bridges, and ourselves when we are on stilts. This excellent description
of Struts reflect the role the Struts plays in developing web applications.
Do we need to pay the Struts if being used in commercial purpose?
No. Struts is available for commercial use at no charge under the Apache Software
License. You can also integrate the Struts components into your own framework just as if
they were writtern in house without any red tape, fees, or other hassles
What are the core classes of Struts?
Action, ActionForm, ActionServlet, ActionMapping, ActionForward are basic classes of
Structs.
What is the design role played by Struts?
The role played by Structs is controller in Model/View/Controller(MVC) style. The View
is played by JSP and Model is played by JDBC or generic data source classes. The Struts
controller is a set of programmable components that allow developers to define exactly how
the application interacts with the user.
How Struts control data flow?
Struts implements the MVC/Layers pattern through the use of ActionForwards and
ActionMappings to keep control-flow decisions out of presentation layer.
What configuration files are used in Struts?
--ApplicationResourcesl.properties
--struts-config.xml
These two files are used to bridge the gap between the Controller and the Model.
Is Struts efficient?
--The Struts is not only thread-safe but thread-dependent(instantiates each Action once
and allows other requests to be threaded through the original object.
--ActionForm beans minimize subclass code and shorten subclass hierarchies
--The Struts tag libraries provide general-purpose functionality
--The Struts components are reusable by the application
--The Struts localization strategies reduce the need for redundant JSPs
--The Struts is designed with an open architecture--subclass available
--The Struts is lightweight (5 core packages, 5 tag libraries)
--The Struts is open source and well documented (code to be examined easily)
--The Struts is model neutral
What is Jakarta Struts Framework? - Jakarta Struts is open source implementation of
MVC (Model-View-Controller) pattern for the development of web based applications.
Jakarta Struts is robust architecture and can be used for the development of application of
any size. Struts framework makes it much easier to design scalable, reliable Web
applications with Java.
What is ActionServlet?
The class org.apache.struts.action.ActionServlet is the called the ActionServlet. In
the the Jakarta Struts Framework this class plays the role of controller. All the requests to
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the server goes through the controller. Controller is responsible for handling all the
requests.
How you will make available any Message Resources Definitions file to the Struts
Framework Environment?
Message Resources Definitions file are simple .properties files and these files contains the
messages that can be used in the struts project. Message Resources Definitions files can be
added to the struts-config.xml file through <message-resources /> tag.
Example:
<message-resources parameter=”MessageResources” />
What is Action Class?
The Action Class is part of the Model and is a wrapper around the business logic. The
purpose of Action Class is to translate the HttpServletRequest to the business logic. To use
the Action, we need to Subclass and overwrite the execute() method. In the Action Class
all the database/business processing are done. It is advisable to perform all the database
related stuffs in the Action Class. The ActionServlet (commad) passes the parameterized
class to Action Form using the execute() method. The return type of the execute method is
ActionForward which is used by the Struts Framework to forward the request to the file as
per the value of the returned ActionForward object.
Write code of any Action Class?
Here is the code of Action Class that returns the ActionForward object.
1. import javax.servlet.http.HttpServletRequest;
2. import javax.servlet.http.HttpServletResponse;
3. import org.apache.struts.action.Action;
4. import org.apache.struts.action.ActionForm;
5. import org.apache.struts.action.ActionForward;
6. import org.apache.struts.action.ActionMapping;
7.
8. public class TestAction extends Action
9. {
10. public ActionForward execute(
11. ActionMapping mapping,
12. ActionForm form,
13. HttpServletRequest request,
14. HttpServletResponse response) throws Exception
15. {
16. return mapping.findForward("testAction");
17. }
18. }
What is ActionForm?
An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm.
ActionForm maintains the session state for web application and the ActionForm object is
automatically populated on the server side with data entered from a form on the client
side.
What is Struts Validator Framework?
Struts Framework provides the functionality to validate the form data. It can be use
to validate the data on the users browser as well as on the server side. Struts
Framework emits the java scripts and it can be used validate the form data on the client
browser. Server side validation of form can be accomplished by sub classing your From
Bean with DynaValidatorForm class. The Validator framework was developed by David
Winterfeldt as third-party add-on to Struts. Now the Validator framework is a part of
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Jakarta Commons project and it can be used with or without Struts. The Validator
framework comes integrated with the Struts Framework and can be used without doing
any extra settings.
Give the Details of XML files used in Validator Framework?
The Validator Framework uses two XML configuration files validator-rules.xml and
validation.xml. The validator-rules.xml defines the standard validation routines, these
are reusable and used in validation.xml. to define the form specific validations. The
validation.xml defines the validations applied to a form bean.
How you will display validation fail errors on jsp page? The following tag displays
all the errors:
<html:errors/>
How you will enable front-end validation based on the xml in validation.xml? The
<html:javascript> tag to allow front-end validation based on the xml in
validation.xml. For example the code: <html:javascript formName=”logonForm”
dynamicJavascript=”true” staticJavascript=”true” /> generates the client side
java script for the form “logonForm” as defined in the validation.xml file. The
<html:javascript> when added in the jsp file generates the client site validation
script.
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EJB Enterprise Java BeansEnterprise Java Beans
Agenda
•What is an EJB
•Bean Basics
•Component Contract
•Bean Varieties
–Session Beans
–Entity Beans
–Message Driven Beans
) Stateful Session Beans : These beans have internal states. They can be stored
(getHandle()) and restored (getEJBObject()) across client sessions.Since they can be
persistence, they are also called as Persistence Session Beans.
Stateless Session Bean:Consider this as a servlet equivalent in EJB. It is just used to
service clients regardless of state and does not maintain any state.
a) Stateless Session Beans : These beans do not have internal States. They need not be
passivated. They can be pooled into service multiple clients.
What is the difference between Stateful session bean and Stateless session bean
Stateful:
 Stateful s.Beans have the passivated and Active state which the Stateless bean does not
have.
 Stateful beans are also Persistent session beans. They are designed to service business
processes that span multiple method requests or transactions.
 Stateful session beans remembers the previous requests and reponses.
 Stateful session beans does not have pooling concept.
 Stattless session bean instances are pooled.
 Stateful Session Beans can retain their state on behave of an individual client.
 Stateful Session Beans can be passivated and reuses them for many clients.
 Stateful Session Bean has higher performance over stateless sessiob bean as they are
pooled by the application server.
Stateless:
 Stateless Session Beans are designed to service business process that last only for a single
method call or request.
 Stateless session beans do not remember the previous request and responses.
 Stateless Session Beans donot maintain states.
 Stateless Session Beans, client specific data has to be pushed to the bean for each method
invocation which result in increase of network traffic.
What is the life cycle of Stateful session bean
Stateful Session Bean has three states. Does not exists, Method Ready and Passivated
states.
Like Stateless beans, when the Stateful Session Bean hasnt been instantiated yet
(so it is not an instance in memory) is it in the Does not exists state.
Once a container creates one or more instances of a Stateful Session Bean it sets
them in a Method Ready state. In this state it can serve requests from its clients. Like
Stateless Session Beans, a new instance is created (Class.newInstance()), the context is
passed (setSessionContext()) and finally the bean is created with ejbCreate().
During the life of a Stateful Session Bean, there are periods of inactivity. In these
periods, the container can set the bean to the Passivate state. This happens through the
ejbPassivate() method. From the Passivate state the bean can be moved back to the
Method Ready state, via ejbActivate() method, or can go directly to the Does Not Exists
state with ejbRemove().
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What is the life cycle of Stateless session bean
Stateless session bean has only two states: Does Not Exists and Method Ready Pool.
A bean has not yet instantiated (so it is not an instance in memory) when it is in the
Does Not Exists state.
When the EJB container needs one or more beans, it creates and set them in the
Method Ready Pool state. This happens through the creation of a new instance
(Class.newInstance()), then it is set its context (setSessionContext()) and finally calls the
ejbCreate() method.
The ejbRemove() method is called to move a bean from the Method Ready Pool back
to Does Not Exists state.
What are the call back methods in Session bean
Session bean callback methods differ whether it is Stateless or stateful Session bean. Here
they are.
Stateless Session Bean
1. setSessionContext()
2. ejbCreate()
3. ejbRemove()
Stateful Session Bean
1. setSessionContext()
2. ejbCreate()
3. ejbPassivate()
4. ejbActivate()
5. ejbRemove()
When you will chose Stateful session bean and Stateless session bean
Stateful session bean is used when we need to maintain the client state . Example of
statefull session is Shoping cart site where we need to maintain the client state .
stateless session bean will not have a client state it will be in pool.
To maintain the state of the bean we prefer stateful session bean and example is to get
mini statement in
ATM we need sessions to be maintained.
What is Entity Bean. What are the various types of Entity Bean
Entity bean represents the real data which is stored in the persistent storage like Database
or file system. For example, There is a table in Database called Credit_card. This table
contains credit_card_no,first_name, last_name, ssn as colums and there are 100 rows in
the table. Here each row is represented by one instance of the entity bean and it is found
by an unique key (primary key) credit_card_no.
There are two types of entity beans.
1) Container Managed Persistence(CMP)
2) Bean Managed Presistence(BMP)
What is the difference between CMP and BMP
CMP means Container Managed Persistence. When we write CMP bean , we dont need
to write any JDBC code to connect to Database. The container will take care of connection
our enitty beans fields with database. The Container manages the persistence of the bean.
Absolutely no database access code is written inside the bean class.
BMP means Bean Managed Persistence. When we write BMP bean, it is programmer
responsiblity to write JDBC code to connect to Database.
What is the lifecycle of Entity Bean
The following steps describe the life cycle of an entity bean instance
An entity bean instances life starts when the container creates the instance using
newInstance and then initialises it using setEntityContext.
The instance enters the pool of available instances. Each entity bean has its own pool.
While the instance is in the available pool, the instance is not associated with any particular
entity object identity. Any of these pooled instances may be used to execute finder
(ejbFind) or home (ejbHome) methods.
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An instance transitions from the pooled state to the ready state when the container
selects that instance to service a client call to an entity object. There are two possible
transitions from the pooled to the ready state: through the creation of an entity (ejbCreate
and ejbPostCreate) or through the activation of an entity (ejbActivate).
When an entity bean instance is in the ready state, the instance is associated with a
specific entity object identity. While the instance is in the ready state, the container can
synchronize the instance with its representation in the underlying data source whenever it
determines the need to using ejbLoad and ejbStore methods. Business methods can also be
invoked zero or more times on an instance. An ejbSelect method can be called by a
business method, ejbLoad or ejbStore method.
The container can choose to passivate an entity bean instance within a transaction.
To passivate an instance, the container first invokes the ejbStore method to allow the
instance to prepare itself for the synchronization of the database state with the instance’s
state, and then the container invokes the ejbPassivate method to return the instance to the
pooled state.
There are three possible transitions from the ready to the pooled state: through the
ejbPassivate method, through the ejbRemove method (when the entity is removed), and
because of a transaction rollback for ejbCreate, ejbPostCreate,or ejbRemove.
The container can remove an instance in the pool by calling the unsetEntityContext()
method on the instance.
What are the call back methods in Entity bean
Entity Bean:
1. setEntityContext()
2. ejbCreate()
3. ejbPostCreate()
4. ejbActivate()
5. ejbPassivate()
6. ejbRemove()
7. unsetEntityContext()
When you will chose CMP and BMP
BMP
- Bean managed persistence
- Developer has to write persistence code for ejbLoad(),ejbStore() for entity beans
- Should follow this approach only when its bare necessity to write your own persistence
logic.Usually container managed persistence is quite sufficient and less error prone.
CMP
- Container managed persistence
- Developer maps the bean fields with the database fields in the deployment descriptors.
- Developer need not provide persistence logic (JDBC) within the bean class.
- Containiner manages the bean field to DB field synchronization.
The point is only ENTITY beans can have theier pesristence mechanism as CMP or
BMP. Session beans, which usually contains workflow or business logic should never have
persistence code.Incase you choose to write persistence within your session bean, its
usefull to note that the persistence is managed by the container BMP.Session beans cannot
be CMP and its not possibel to provide field mapping for session bean.
BMPs are much harder to develop and maintain than CMPs.All other things are being
equal,choose CMPs over BMPs for pure maintainability.
There are limitations in the types of the data sources that may be supported for
CMPs by a container provide.Support for non JDBC type data sources,such as CICS,are not
supported by the current CMP mapping and invocation schema.Therefore accessing these
would require a BMP.
Complex queries might not be possible with the basic EJBQL for CMPs.So prefer
BMPs for complex queries.
If relations between entity beans are established then CMPs may be necessary.CMR
has ability to define manage relationships between entity beans.
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Container will tyr to optimize the SQL code for the CMPs,so they may be scalable
entity beans than the BMPs.
BMPs may be inappropriate for larger and more performance sesitive applications.
What are advantages and disadvantages of CMP and BMP
CMP: Container managed persistence
Advantages:
1)Easy to develop and maintain.
2)Relationships can be maintained between different entities.
3)Optimization of SQL code will be done.
4)Larger and more performance applications can be done.
Disadvantages:
1)Will not support for some nonJDBC data sources,i.e,CICS.
2)Complex queries cannot be developed with EJBQL.
BMP:: Bean managed persistence
Advantages:
1)Support for nonJDBC data sources.
2)Complex queries can be build.
Disadvantages:
1)Hard to develop and maintain.
2)We cannot maintain the relationships between different entities.
3)Optimization of SQL code cannot be done by the container,because bean it self contains
the code.
4)Not appropriate for larger and complex applications.
What is difference between EJB 1.1 and EJB 2.0
EJB 2.0 adds the local beans, which are accessible only from within the JVM where beans
are running in.
In EJB 1.1, we had to implement remote client views for all these beans, even if we had no
remote clients.
What is Message Driven Bean
Message Driven Bean (MDB) is an enterprise bean which runs inside the EJB container and
it acts as Listener for the JMS asynchronous message . It does not have Home and Remote
interface as Session or Entity bean. It is called by container when container receives JMS
asynchronous message. MDB has to implement MessageListener which has a method
onMessage(Message msg). When the container calls the MDB it passes the message to
onMesage() method and then MDB process that message.
What is the life cycle of MDB
The lifetime of an MDB instance is controlled by the container. Only two states exist: Does
not exist and Ready , as illustrated in the following figure:
The life of an MDB instance starts when the container invokes newInstance() on the
MDB class to create a new instance. Next, the container calls setMessageDrivenContext()
followed by ejbCreate() on the instance. The bean then enters the Ready state and is ready
to consume messages.
When a message arrives for the bean, the container invokes the onMessage()
method of one of the available instances, passing a Message object in argument. Message s
can be consumed and processed concurrently by using multiple instances of the same type.
The container invokes ejbRemove() on the bean instance when it no longer needs
the instance. The bean instance can perform clean up operations here.
What is local interface. How values will be passed
If Client and EJB classes are in the same machine ( Same JVM) then we can use Local
linterface instead of Remote interface. Since Client and EJB are in same JVM, values are
passed by referance.
What is the difference between local interface and remote interface
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We can describe the following common rules for choosing whether to use remote client view
or local client view:
When you will potentially use a distributed environment (if your enterprise bean should
be independent of its deployment place), you should obviously choose remote client view.
Use remote client view when you need to be sure that parameters passed between your
EJB and the client (and/or other enterprise beans) should be passed "by value" instead of
"by reference." With pass-by-value, the bean will have its own copy of the data, completely
separated from the copy of the data at the client. With local client view, you can do pass-
by-reference, which means your bean, as well as the client, will work directly with one copy
of the data. Any changes made by the bean will be seen by the client and vice versa. Pass-
by-reference eliminates time/system expenses for copying data variables, which provides a
performance advantage.
If you create an entity bean, you need to remember that it is usually used with a
local client view. If your entity bean needs to provide access to a client outside of the
existing JVM (i.e., a remote client), you typically use a session bean with a remote client
view. This is the so-called Session Facade pattern, the goal of which is that the session
bean provides the remote client access to the entity bean.
If you want to use container-managed relationship (CMR) in your enterprise bean, you
must expose local interfaces, and thus use local client view. This is mentioned in the EJB
specification.
Enterprise beans that are tightly coupled logically are good candidates for using local
client view. In other words, if one enterprise bean is always associated with another, it is
perfectly appropriate to co-locate them (i.e., deploy them both in one JVM) and organize
them through a local interface.
What is EJB Query Language
EJB QL is somewat similar to SQL. But ejb ql is used to retrieve data from bean objects
where as sql is used to retrieve data from tables.
What is ACID
ACID is releated to transactions. It is an acronyam of Atomic, Consistent, Isolation and
Durable. Transaction must following the above four properties to be a better one
Atomic: It means a transaction must execute all or nothing at all.
Consistent: Consistency is a transactional characteristic that must be enforced by both the
transactional system and the application developer
Isolation: Transaation must be allowed to run itselft without the interference of the other
process or transactions.
Durable: Durablity means that all the data changes that made by the transaction must be
written in some type of physical storage before the transaction is successfully completed.
This ensures that transacitons are not lost even if the system crashes.
What are the various isolation levels in a transaction and differences between
them
There are three isolation levels in Transaction. They are
1. Dirty reads 2.Non repeatable reads 3. Phantom reads.
Dirrty Reads: If transaction A updates a record in database followed by the transaction B
reading the record then the transaction A performs a rollback on its update operation, the
result that transaction B had read is invalid as it has been rolled back by transaction A.
NonRepeatable Reads :If transaction A reads a record, followed by transaction B
updating the same record, then transaction A reads the same record a second time,
transaction A has read two different values for the same record.
Phantom Reads :If transaction A performs a query on the database with a particular
search criteria (WHERE clause), followed by transaction B creating new records that satisfy
the search criteria, followed by transaction A repeating its query, transaction A sees new,
phantom records in the results of the second query.
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What is the difference between activation and passivation
Activation and Passivation is appilicable for only Stateful session bean and Entity bean.
When Bean instance is not used for a while by client then EJB Container removes it
from memory and puts it in secondary storage (often disk) so that the memory can be
reused. This is called Passivation.
When Client calls the bean instance again then Container takes the passivated bean
from secondary storage and puts it in memory to serve the client request. This is called
Activation.
What is Instance pooling
pooling of instances.
in stateless session beans and Entity Beans server maintains a pool of instances.whenever
server got a request from client, it takes one instance from the pool and serves the client
request.
What is the difference between HTTPSession and Stateful Session Bean
From a logical point of view, a Servlet/JSP session is similar to an EJB session. Using a
session, in fact, a client can connect to a server and maintain his state.
But, is important to understand, that the session is maintained in different ways and, in
theory, for different scopes.
A session in a Servlet, is maintained by the Servlet Container through the HttpSession
object, that is acquired through the request object. You cannot really instantiate a new
HttpSession object, and it does not contains any business logic, but is more of a place
where to store objects.
A session in EJB is maintained using the SessionBeans. You design beans that can
contain business logic, and that can be used by the clients. You have two different session
beans: Stateful and Stateless. The first one is somehow connected with a single client. It
maintains the state for that client, can be used only by that client and when the client
"dies" then the session bean is "lost".
A Stateless Session Bean does not maintain any state and there is no guarantee that
the same client will use the same stateless bean, even for two calls one after the other. The
lifecycle of a Stateless Session EJB is slightly different from the one of a Stateful Session
EJB. Is EJB Containers responsability to take care of knowing exactly how to track each
session and redirect the request from a client to the correct instance of a Session Bean. The
way this is done is vendor dependant, and is part of the contract.
What is the difference between find and select methods in EJB
select method is not there in EJBs
A select method is similar to a finder method for Entity Beans, they both use EJB-QL to
define the semantics of the method.
They differ in that an ejbSelect method(s) are not exposed to the client and the ejbSelect
method(s) can return values that are defined as cmp-types or cmr-types.
What are the optional clauses in EJB QL
Three optional clauses are available in EJB Ql.
1. SELECT
2. FROM
3. WHERE
The EJB QL must always contain SELECT and FROM clauses. The WHERE clause is
optional.
The FROM clause provides declarations for the identification variables based on abstract
schema name, for navigating through the schema. The SELECT clause uses these
identification variables to define the return type of the query, and the WHERE clause
defines the conditional query.
What is handle in EJB
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To get hold the session state of the Stateful Session bean.
A handle is an abstraction of a network reference to an EJB object. A handle is intended to
be used as a "robust" persistent reference to an EJB object.
What is the difference between JNDI context, Initial context, session context and
ejb context
JNDI Context Provides a mechanism to lookup resources on the network
Initial Context constructor provides the initial context.
Session Context has all the information a session bean would require from the container
Entity Context has all the information that an Entity bean would need from a container
Ejb Context contains the information that is common to both the session and entity bean
What is the difference between sessioncontext and entitycontext
Session Context Contains information that a Session Bean would require from the container
Entity Context contains the information that an Entity Bean would require from a container
What is deployment descriptor
Deployment Descriptor is a XML document with .xml extenion. It basically descripes the
deployment settings of an application or module or the component. At runtime J2EE server
reads the deployment descriptor and understands it and then acts upon the component or
module based the information mentioned in descriptor.
For example EJB module has a deployment descriptor ejb-jar.xml where we mention
whether it is session or entity or mesage driven bean and where is the home, remore and
Bean classes are located and what type of transaction etc. In a simple word, without
deployment descritor the Container ( EJB/Servlet/JSP container) will not know what to do
with that module.
What is CMR
CMR - Container Managed Relationships allows the developer to declare various types of
relationships between the entity beans
What is the difference between CMP 1.1 and CMP 2.0
CMR and sub classing of the CMP bean by the container
What is the difference between optimistic locking and pessimistic locking
Optimistic locking assumes that no one would read or change the data while changes are
being by a bean
Pessimistic locking would rather lock down the data so that no one can access it
What is lazy loading
Lazy loading is a characteristic of an application when the actual loading and instantiation of
a class is delayed until the point just before the instance is actually used. The goal is to only
dedicate memory resources when necessary by only loading and instantiating an object at
the point when it is absolutely needed.
Tools such as Eclipse have popularized the lazy-loading approach as they use
the facility to control the load and initialization of heavyweight plug-ins. This gives the
double bonus of speeding up the initial load time for the application, as not all plug-ins are
loaded straightaway; ensuring efficiency as only the plug-ins that are used are loaded at all.
Is Decorator an EJB design pattern
No , If i throw a custom ApplicationException from a business method in Entity bean which
is participating in a transaction, would the transaction be rolled back by container. Does
container rolls back transaction only in case of SystemExceptions
Yes, the rollback will occur For declarative transactions, container will rollback on
systemException. Container has no way to know whether a speicific application exception is
serious enough to roll back the participated transaction. Use setRollbackOnly() to doom the
transaction.
What are simple rules that a Primary key class has to follow
Implement the equals and hashcode methods.
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JAVA & J2EE
What is abstract schema
CMP uses abstract schema to map to the physical database
What is re-entrant. Is session beans reentrant. Is entity beans reentrant
Re-entrant means where Bean A calls methods of Bean B and then Bean B turns around
and calls methods of Bean A. The above all within a single thread of control. This is also
called as loopback.
Entity beans are the only one bean that is reentrant. Neither Session bean nor
Message Driven Bean are reentrant. When Entity bean, we have to declare in the
deployment descriptor whether it is reentrant ( true or false).
Why an onMessage call in Message-driven bean is always a seperate transaction
The MDB is stateless and inherently each message is unique with respect to the MDB.
Each message needs to be processed independently. Hence the need for separate
transactions
Does Stateful Session bean support instance pooling
All Beans support Instance Pooling
statefull session bean does not maintain instance pooling,
stateless session beans and entity beans can maintain instance pooling
Why does EJB needs two interfaces(Home and Remote Interface)
Home is to provide Lookup from JNDI while Remote is to provide Object Instantiated
Can I invoke Runtime.gc() in an EJB
No
Can a Session Bean be defined without ejbCreate() method
No
Why are ejbActivate() and ejb Passivate() included for stateless session bean
even though they are never required as it is nonconversational bean
To have a consistent interface, so that there is no different interface that you need to
implement for Stateful Session Bean and Stateless Session Bean. Both Stateless and
Stateful Session Bean implement javax.ejb.SessionBean and this would not be possible if
stateless session bean is to remove ejbActivate and ejbPassivate from the interface. You
could argue that the two (stateful and stateless) are so different that they should have their
own interface but Sun did not think so. They made both session beans implement the same
interface and provided deployment descriptor to denote which one is it that you are
deploying.
With EJB 1.1 specs, why is unsetSessionContext() not provided in Session
Beans, like unsetEntityContext() in Entity Beans
This was the answer Provided by some one... According to Mohan this one is not
correct. Please see Mohan's reply below and more in the comments section.
ejbRemove() is called for session beans every time the container destroyes the bean. So
you can use this method to do the stuff you typically would do in unsetEntityContext(). For
entity beans ejbRemove() is only called if the user explicitly deletes the bean. I think that is
the reason why the engineers at SUN invented the unsetEntityContext() for this kind of
bean.
What is the difference between ejbStore() and ejbLoad()
When the EJB container needs to synchronize the instance variables of an entity bean with
the corresponding values stored in a database, it invokes the ejbLoad and ejbStore
methods. The ejbLoad method refreshes the instance variables from the database, and the
ejbStore method writes the variables to the database. The client cannot call ejbLoad and
ejbStore.
What is the difference between ejbCreate() and ejbPostCreate()
Session and Message Driven Bean will have only ejbCreate() method and no
ejbPostCreate() method. Entity bean will have both ejbCreate() and ejbPostCreate()
methods.
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JAVA & J2EE
The ejbPostCreate method returns void, and it has the same input parameters as
the ejbCreate method. If we want to set a relationship field to initialize the bean instance,
we should do so in the ejbPostCreate method. we cannot set a relationship field in the
ejbCreate method.
The ejbPostCreate() allows the bean to do any post-create processing before it
begins serving client requests. For every ejbCreate() there must be a matching (matching
arguments) ejbPostCreate() method.
Is stateless Sessiob bean create() method contains any parameters
No. This method must not contain any input parameters and cannot be overloaded as well.
How can i retrieve from inside my Bean(Stateless session and Entity CMP) the
user name which i am serving (the user name of user just logged in my web
application)
Inside an EJB you may retrieve the "Caller" name, that is the login id by invoking:
sessionContext.getCallerIdentity().getName() where sessionContext is the instance of
"SessionContext" (setSessionContext) passed to the Session Bean, or the instance of
"EntityContext" (setEntityContext) passed to the Entity Bean.
What is EJB architecture(components)
EJB Architecture consists of :
a) EJB Server
b) EJB containers that run on these servers,
c) Home Objects, Remote EJB Objects and Enterprise Beans that run within these
containers,
d) EJB Clients and
e) Auxillary systems like JNDI (Java Naming and Directory Interface), JTS(Java Transaction
Service) and security services.
If my session bean with single method insert record into 2 entity beans, how
can I know that the process is done in same transaction (the attributes for these beans are
Required)
If your method in the session bean is already running under a transaction the calls to any
other bean which have been deployed with trans-attribute 'Required' will be executed within
the same transaction context.
So if your session bean is using container-managed transactions and your
method is deployed with 'Required', 'RequiresNew' or 'Mandatory', you can safely assume
that the calls to your entity beans are handled under same transaction. If you're not
running in a transaction, a separate transaction will be set up for each call to your entity
beans.
If your session bean is using bean-managed transactions, you can ensure that the calls are
handled in the same transaction by :
javax.transaction.UserTransaction tran= null;
try{
tran=ctx.getUserTransaction();
tran.begin();
myBeanHome1.create(....);
myBeanHome2.create(...);
tran.commit();
}catch(...){}
You may want to check if you're already running in a transaction by calling
tran.getStatus().
Is there a way to get the original exception object from inside a nested or
wrapped Exception (for example an EJBException or RemoteException)
Absolutely yes, but the way to do that depends on the Exception, since there are no
standards for that. Some examples: ·When you have an javax.ejb.EJBException, you can
use the getCausedByException() that returns a java.lang.Exception. ·A
java.rmi.RemoteException there is a public field called detail of type java.lang.Throwable
·With a java.sql.SQLException you need to use the method getNextException() to get the
chained java.sql.SQLException. ·When you have an
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JAVA & J2EE
java.lang.reflect.InvocationtargetException, you can get the thrown target
java.lang.Throwable using the getTargetException() method.
Can undefined primary keys are possible with Entity beans?If so, what type is
defined?
Yes,undefined primary keys are possible with Entity Beans.The type is defined as
java.lang.Object.
When two entity beans are said to be identical?Which method is used to compare
identical or not?
Two Entity Beans are said to be Identical,if they have the same home inteface and their
primary keys are the same.To test for this ,you must use the component inteface's
isIdentical() method.
Why CMP beans are abstract classes?
We have to provide abstract data to object mapping that maps the fields in our bean to a
batabase, and abstract methods methods that corelate these fields.
Is instance pooling necessary for entity beans?
One of the fundamental concepts of Entity Beans is that they are the pooled
objects.Instance pooling is the service of the container that allows the container to reuse
bean instances,as opposed to creating new ones every time a request for a bean is
made.This is a perfomance optimizatio done by the container.
What is the difference b/w sendRedirect() and <jsp: forward>?
sendredirect will happen on clint side & request , rsponse will be newly created, for forward
action it is server side action & request, response is passed & not modified or destroyed.
How the abstract classes in CMP are converted into concrete classes?
EJB2.0 allows developer to create only abstract classes and at the time of deployement the
container creates concrete classes of the abstract. It is easy for container to read abstract
classes and appropriately generate concrete classes.
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