Overview of JEE Technology

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Overview of JEE Technologies

Objectives
In this session, you will learn to:
Describe website and Web application
Identify Enterprise Application
Explore Servlet API

A Web page is an electronic document, which is created using HTML
and is translated by the Web browser.
A Web pages can be :
Static
Dynamic
A website is a collection of one or more Web pages, which are hosted
on a Web server and are accessed by using client applications, such as a
Web browser.
A Website usually refers to the front-end interface through which the
users interacts with a business online.
A website consists of:
HTML and other graphic files
Audio and Video files
Other static files
Describing a Website and Web Application

A Web application:
Is a program that is stored on a remote server and delivered over the
Internet through a Web browser using various protocols, such as HTTP.
Is a Website with dynamic functionality on the server and can be
controlled by the users.
To access a Web application:
A client sends a request to the Web server.
A Web server processes the request, generates the response, and sends
the response to the client.
Describing a Website and Web Application (Contd.)

What is an enterprise
application?
Identifying an Enterprise Application

An enterprise application is the term used to describe applications or
software that a business would use to assist the organization in solving
enterprise problems.
An enterprise application is an application that is:
Large in size
Distributed
Secure and scalable
Highly available
Accessible through multiple types of clients
Important aspects of an enterprise application are:
Presentation logic
Business logic
Data Access logic
System Services
Identifying an Enterprise Application (Contd.)

Java Enterprise Edition:
Is Oracle's enterprise Java computing platform.
Is built upon the foundation of Java Platform, Standard Edition (Java SE).
Is an open and standard based platform for developing, deploying, and
managing n-tier, Web-enabled, server-centric, and
component-based enterprise applications.
It consists of a set of services, APIs, and protocols that provide the
functionality for developing multitier, Web-based applications.
Is a collection of related technology specifications that describe
required APIs and policies.
Identifying Java Enterprise Edition (EE)

Identifying the Features of Java EE
Java EE comprises the following features:
Client tier support:
 J2EE supports pure HTML, as well as Java applets or applications.
 It relies on Java Server Pages and servlet code to create HTML or other formatted
data for the client.
Middle Layer support:
 J2EE supports Enterprise JavaBeans (EJBs) as middle layer, where the platform's
logic is stored.
Java Database Connectivity (JDBC):
 J2EE supports JDBC, which is the Java equivalent to ODBC.
JavaMail API:
 It consists of libraries to create, send, receive, and read email messages.
 It enables the J2EE applications to handle mail messages easily.
 It supports the IMAP4, POP3, and SMTP mail protocols.

Identifying the Features of Java EE (Contd.)
Java Naming and Directory Interface (JNDI) API:
 It enables application components and clients to search and link distributed
resources, services, and EJB components.
 It allows the configuration of external and custom resources in the Sun ONE
Application Server.
Java Message Service (JMS) API:
 It enables the J2EE applications to create, send, receive, and read messages in a
distributed environment.
 It uses JMS queues, topics, and message destinations, which are made available
using the JNDI API.

Identifying Various Types of Java EE Container
Various types of Java EE containers are:
Web container: Provides a runtime environment to manage deployed Web
components, such as servlets and JSP.
Applet container: Provides the runtime environment for executing applets.
EJB container: Provides a runtime environment to manage deployed EJB
components.
Application client container: Provides a runtime environment for Java EE
application clients.
The following figure depicts the interaction between different Java EE
containers.
Application
client container
Applet container
Web container
EJB container
Database

Identifying JAR, WAR, and EAR
In J2EE application, modules are packaged as Java archive (JAR), Web
archive (WAR), and Enterprise archive (EAR) based on their functionality.
JAR:
Is a package file format that is used to group Java class files and associated
metadata and resources into one file.
Is used to distribute application software or libraries on the Java platform.
WAR:
Is used to package a Web application, which is a group of JSP, HTML, servlets,
resources and source files.
Includes a Web deployment descriptor file and can be used to import a Web
application into a Web server.
EAR:
Is used by Java EE for packaging one or more modules into a single archive.
Is used to enable the deployment of the various modules onto an
application simultaneously and coherently.

Identifying Various Java EE APIs and Technologies
Java EE comprises of the following APIs and technologies:
Standard Edition (Java SE)
Java Servlets
Java Server Pages™ (JSP™)
Java Server Faces™ (JSF™)
Remote Method Invocation (RMI)
Java Persistence API (JPA)
Java Message Service (JMS) API
Java Naming and Directory Interface™ (JNDI) API
Java Transaction API (JTA)
Enterprise JavaBeans™ (EJB™) components
Java API for XML Web Services (JAX-WS)

Identifying Java Servlet
A Servlet is a Java program that runs on a server and used to
generate dynamic Web pages.
Servlets performs the following tasks:
Processes HTTP requests
Generates dynamic HTTP responses
Servlets act as a middle layer between a request coming from a
Web browser or other HTTP client and databases.
Servlets executes inside a Web container as a thread.
The following figure depicts the position of the servlet in a Web
application.
HTTP Server
Web Browser
Servlet Program
Database
HTTP
Protocol

Identifying the Advantages of Java Servlet
Some of the advantages of Java servlets are:
Servlets are faster than CGI programs because each scripts in CGI
produces a new process and these processes takes a lot of time for
execution. However, servlets creates only new thread.
Servlets are server side components that inherits the security
provided by the Web server and Java Security Manager.
Servlets provide all the powerful features of Java, such as exception
handling and garbage collection.
Servlets are portable across operating systems and across Web
servers as servlets are write once, run anywhere (WORA) programs
written in Java.
Servlets can share data among each other and can maintain the
session which helps them to maintain information from request to
request.
The servlet API is designed in such a way that it can be easily
extensible.

Identifying the Limitation of Java Servlet
Some of the limitations of Java servlets are:
Whenever a Web page changes, the servlet needs to be rewritten,
recompiled, and redeployed.
Servlets must handle concurrency issues.
Tedious uses of out.println()statements.
Designing in servlet is difficult and slows down the application.
Writing complex business logic makes the application difficult to
understand.

Identify Servlet Terminology
Basic terminologies used in servlet are:
Hypertext Transfer Protocol (HTTP)
HTTP request
HTTP response
Difference between Web server and application server
Web container

Identifying HTTP Protocol
HTTP is a protocol that is used by a client and a server to communicate
with each other.
It supports only one request per connection.
It can be used to transmit any file that follows the Multipurpose
Internet Mail Extensions (MIME) specification.
It uses the request and response process to transfer information from
one computer to another

Identifying HTTP Request
HTTP request is like an envelope, which contains the necessary
information required by the Web server to process a client request.
An HTTP request consists of:
Request line: It contains request method, request URL, and version.
Request header: It contains additional information about the client, such as
the name and the version of the Web browser.
Message body: It is an optional part of the HTTP request. It contains the data
entered by a user that needs processed.
The following figure describes an HTTP request.

Identifying HTTP Response
HTTP response is like an envelope that contains the response generated
by a server that would be displayed by a Web browser.
The HTTP response consists of:
Status line: It consists of status code, reason phrase, and version of the
HTTP protocol.
Response header: It contains additional information about the Web server.
Message body: It consists of the response in the form of Hyper Text Markup
Language (HTML) format.
The following figure describes an HTTP response.

Difference Between the Web Server and Application Server
Web Server Application Server
Web server handles the HTTP
protocol.
Whenever, a Web server receives
an HTTP request, it responds with
an HTTP response.
It may respond with a static HTML
page or image, send or redirect,
or delegate the dynamic response
generation to some other
program such as CGI scripts, JSPs
(Java Server Pages), Servlets.
An application server exposes
business logic to client
applications through various
protocols like HTTP, TCP-IP etc.
An application server providers
allows the client to access the
business logic for use.
An application server is used to
run business logic or dynamically
generating presentation code.
An application server is more
capable of dynamic behavior
than web server.
The following points depicts the differences between the Web server and
Application server:

Identifying Web Container
What is a Web container?

Identifying Web Container (Contd.)
Web container is a Java virtual machine
that supplies an implementation of the
Java Servlet API.
All Java servlets must exist in the Web
container.
Web Container activate the servlet that
match to request.

The following figure depicts how the Web container handles the client
request.
Web server
Client
Web
container
Servlet
Thread
Service()
doGet()
<html>
<body>
-----------
</body>
</html>
Identifying Web Container (Contd.)

Execution Process of Java Servlets
Following steps illustrates how a Java servlet executes:
1. The client sends request to the server.
2. The Web container, running inside the server, receives the request.
3. The Web container creates a new thread to process the request.
4. The Web container forwards the request to the servlet.
5. The Web container executes the servlet.

Execution Process of Java Servlets (Contd.)
The following figure depicts the execution process of a servlet
with a single request.

Execution Process of Java Servlets (Contd.)
The following figure depicts the execution process of a servlet
with multiple requests.
Processor’s load does not increase much on execution of multiple
requests.

Exploring Servlet API (Contd.)
Servlet API:
is used to create and manage servlets.
consists of various interfaces, classes, and methods.
classes and methods are available in the following packages:
 javax.servlet
 javax.servlet.http

The following figure depicts the class hierarchy of the Servlet API.
Servlet API
ServletException
Javax.servlet.http
Servlet
ServletConfig
ServletContext
ServletRequest
ServletResponse
AsyncContext
Javax.servlet
GenericServlet
Cookie
HttpServletRequest
HttpServletResponse
HttpSession
HttpServlet
Packages
Classes
Interfaces
RequestDispatcher

The javax.servlet package:
consists of the following interfaces, as described in the table.
Interface Description
Servlet It provides the methods that all servlets must implement.
ServletConfig It provides information to the servlets during the servlet
initialization.
ServletContext It provides methods, which is used by the servlets to
communicate with the Web container.
ServletRequest It provides the client request information to the servlet.
ServletResponse It helps the servlet in sending the response to the client.
RequestDispatcher It receives a request from a client and sends it to any other
resource, such as a servlet, an HTML page, or a JSP page.
AsyncContext It provides the methods to handle multiple client requests
asynchronously.

The Servlet interface methods are implemented by the servlet class
that extends from a GenericServlet or HttpServlet class.
The following table describes the various methods defined in the
Servlet interface:
Method Description
void init(ServletConfig config)
throws ServletException
It is called by the servlet container to indicate
to a servlet that the servlet is being placed
into service.
ServletConfig getServletConfig() Returns a ServletConfig object, which
contains initialization and startup parameters
for this servlet.
String getServletInfo() Returns information about the servlet, such as
author, version, and copyright.
void service(ServletRequest request,
ServletResponse response) throws
ServletException, IOException
It is Called by the servlet container to allow
the servlet to respond to a request.
void destroy() Called by the servlet container to indicate to a
servlet that the servlet is being taken out of
service.

ServletRequest interface:
Method Description
public String getParameter(String
paramName)
Returns a String object that specifies the
value of a particular request parameter.
public String[]
getParameterValues(String paramName)
Returns an array of String objects that
contains all the values of the request
parameter.
public Enumeration
getParameterNames()
Returns an Enumeration object containing
all the parameter names as String objects
that `request contains.
public String getRemoteHost() Returns a String object that specifies the
full-qualified name of the computer from
which the request is sent.
public String getRemoteAddr() Returns a String object that specifies the IP
address of the computer from which the
request is sent.

ServletResponse interface:
Method Description
public ServletOutputStream
getOutputStream() throws
IOException
Returns an object of the
ServletOutputStream class that
represents an output stream to send
binary data as response.
public PrintWriter getWriter()
throws IOException
Returns an object of the PrintWriter
class that the servlet uses to send
character data as response.
public void setContentType(String
type)
Sets the MIME type for a servlet response.
Some of the MIME types are text/plain,
image/jpeg, and text/html.

The javax.servlet package:
Consists of the following classes:
 GenericServlet
 ServletException
The GenericServlet class defines a generic, protocol-independent
servlet.
The GenericServlet implements the Servlet and ServletConfig
interfaces .
The ServletException class defines a general exception a servlet can
throw when it encounters difficulty.
The ServletException class contains the following constructors:
 ServletException()
 ServletException(String message)
 ServletException(String message, Throwable rootCause)

The following code illustrates a simple example of servlet by inheriting
the GenericServlet class:
import java.io.*;
import javax.servlet.*;
public class myFirstServlet extends GenericServlet{
public void service(ServletRequest req,
ServletResponse res)throws IOException,
ServletException {
res.setContentType("text/html");
PrintWriter out=res.getWriter();
out.print("<html><body>");
out.print("<b>hello generic servlet</b>");
out.print("</body></html>");
}
}

The javax.servlet.http package:
Provides classes and interfaces that enable you to create a servlet that
communicates using the HTTP protocol.
Provides the HttpServlet class to create servlets, which is an abstract class.
Provides the HttpServlet class that extends the GenericServlet class
and implements Serializable interface.
Provides HTTP specific methods, such as doGet, doPost, and doHead.
Some of the interfaces of the javax.servlet.http package are:`
HttpServletRequest
HttpServletResponse
HttpSession

HttpServletRequest interface:
Method Description
public String getHeader(String
fieldname)
Returns the value of the request header
field, such as Cache-Control and
Accept-Language, specified in the
parameter.
public Enumeration
getHeaders(String sname)
Returns all the values associated with a
specific request header as an enumeration
of String objects.
public Enumeration
getHeaderNames()
Returns the names of all the request
headers that a servlet can access as an
enumeration of String objects.

HttpServletResponse interface:
Method Description
void setHeader(String hname, String
hvalue)
Sets the value of header hname to hvalue. If
the header has already been set, the new
value overwrites the existing value.
void setIntHeader(String hname, int
hvalue)
Sets the value of the header hname to the int
value, hvalue. If the header has already been
set, the new value overwrites the existing
value.
void addHeader(String hname, String
hvalue)
Adds a header hname with value hvalue. This
method adds a new header if the header
already exists.
void addIntHeader(String hname, int
hvalue)
Adds a header hname with an int value,
hvalue.
boolean containsHeader(String hname) Returns true if the header hname has already
been set with a specific value and false, if not.
void sendRedirect(String url) Redirects a request to the specified URL.

HttpSession interface:
Method Description
public void setAttribute(String name,
Object value)
Binds the object with a name and stores the
name/value pair as an attribute of the
HttpSession object. If an attribute already
exists, this method replaces the existing
attribute.
public Object getAttribute(String
name)
Retrieves the String object specified in the
parameter, from the session object. If no
object is found for the specified attribute, the
getAttribute()method returns null.
public Enumeration
getAttributeNames()
Returns an Enumeration object that contains
the name of all the objects that are bound as
attributes to the session object.

The following code illustrates a simple example of servlet by inheriting
the HttpServlet class:
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class myFirstHttpServlet extends HttpServlet
{
public void doGe(HttpServletRequest request,
HttpServletResponse response)throws IOException{
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<body>");
out.println("<h1>Hello Servlet Get</h1>");
out.println("</body>");
out.println("</html>");
}
}

Identifying Servlet Life Cycle
Process the request- service()
Loading servlet, Instantiate and
Initialization - init()
Unload servlets / Take out of
service - destroy()
doGet() or doPost()
Calls
Calls
Calls
The Web container maintains the life cycle of a servlet instance.
The following figure depicts the life cycle of Java servlet.
1. Servlet class is loaded.
2. Servlet instance is created.
3. init()method is invoked.
4. service()method is invoked.
5. destroy()method is invoked.

Implementing a Servlet
To create a servlet, you need to perform the following tasks:
Create a servlet.
Configure the servlet.
Compile and deploy the servlet.
Access the servlet using a browser application.

Creating a Servlet
Servlet can be created by extending the HttpServlet or
GenericServlet class.
Example:
Consider a scenario in which you have to create servlet that displays
the current date to the user, each time the servlet is accessed. To do
this, you have to create a servlet that extends from the HttpServlet
class, as shown in the embedded file.

Configuring a Servlet
Configuring a servlet means, associating a URL with the servlet.
Servlets can be configured using either of the way:
Deployment descriptor (DD)
Annotations
A deployment descriptor is an XML file with the name web.xml that
contains configuration information of a Web application.
Each Web application contains one web.xml file.
The elements of the web.xml file enable you to specify:
Servlet context initialization parameters of a Web application.
Initialization parameter for the servlet.
Mapping between a file extension and a MIME type.
Mapping between a servlet and a URL pattern.
The name of the listener class that responds to a servlet life cycle event.

Configuring a Servlet (Contd.)
Some of the commonly used elements of the web.xml file along with
their usage are:
<servlet>: specifies the configuration details of all the servlets used in a
Web application and contains the following sub elements:
 <servlet-name>
 <servlet-class>
<servlet-mapping>: consists of following sub elements:
 <servlet-name>
 <url-pattern>
<session-config>
<init-param>
<mime-mapping>
Sample DD file:

Configuring a Servlet (Contd.)
Configuring a servlet by using annotations:
The javax.servlet.annotation package defines the @WebServer
annotation that you can use to configure a servlet, as shown in the
following sample code snippet:
@WebServer(name="MyFirstServlet",
urlPatterns={"/MyFirstServlet", "/MyServlet/*"})
public class MyFirstServlet extends HttpServlet
{
…
}
The @WebServer annotation is used to configure the MyFirstServlet
servlet. The name attribute specifies the name of the servlet. The
urlPatterns attribute is used to map the servlet with the URL patterns.

Compile and Deploy the Servlet on Server
To You can compile and deploy your application using your
Eclipse IDE.
Finally, you can access the Web application using the URL, as
shown the following code snippet:
Http://Localhost:8080/myApplication/

Summary
A Web page is an electronic document, which is created using HTML
and is translated by the Web browser.
A website is a collection of one or more Web pages, which are
hosted on a Web server and are accessed by using client
applications, such as a Web browser.
A Web application is a program that is stored on a remote server
and delivered over the Internet through a Web browser using
various protocols, such as HTTP.
An enterprise application is the term used to describe applications
or software that a business would use to assist the organization in
solving enterprise problems.
Java EE is built upon the foundation of Java Platform, Standard
Edition (Java SE).
Web container provides a runtime environment to manage deployed
Web components, such as servlets and JSP.

Summary (Contd.)
Applet container provides the runtime environment for executing
applets.
EJB container provides a runtime environment to manage deployed
EJB components.
Application client container provides a runtime environment for Java
EE application clients.
Java Servlet API consists of two packages:
javax.servlet package
javax.servlet.http package
The various interfaces of javax.servlet package are:
ServletRequest interface
ServletContext interface
ServletResponse interface

Summary (Contd.)
Servlet interface provides the methods that all servlets must
implement.
The GenericServlet class defines a generic, protocol-independent
servlet.
The GenericServlet implements the Servlet and ServletConfig
interfaces .
The ServletException class defines a general exception a servlet can
throw when it encounters difficulty.
The HttpServlet class is used to create a servlets that communicates
using the HTTP protocol.
The HttpServlet class that extends the GenericServlet class and
implements Serializable interface.

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