Basics of Spring - KNOWARTH

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By Dinesh Radadiya
Spring Basics
By Mangalsinh Rajput
© 2014 Knowarth

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 Introduction
 Where we can use spring
 Spring Core Module
 Types of DI [Dependency Injection]
 Factory Methods
 Scope of bean
Agenda
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Introduction
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 Spring provide various level of support for developing
enterprise in Java applications. It simplifies many
different Java EE tasks.
 Spring allows loose coupling between classes so
developer can focus on solving the domain problem.
 To do this, we require someone who manage these
components and it’s dependencies.
Introduction
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Introduction
 This is done by Container which is commonly used in
EE, is also used by Spring and is called “IoC” (Inversion
of Control) Container. Sequential and Parallel
Execution Support.
 Spring provides a Container/Factory which manages
component instantiation and initialization and
component dependencies.

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Where we can use spring
Spring Basics

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Spring Basics
Spring framework can be used to develop end to end
application
DAO
Spring DAO
Using Spring
Support for
JDBC
ORM
Hibernate
JPA
iBatis JEE
JMS
EJBs
WEB
Struts
JSF
Jasper Report
Freemarker
Spring MVC
AOP
Spring AOP
AspectJ Integration
Core
IoC Container

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 In typical Java application we can use Spring in
following various levels.
 Web Layer : Struts 1, Struts2, JSF, Spring MVC
 Business Layer : EJBs, Web Services, Spring
 Domain Layer : Hibernate, Spring JDBC Templates

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 Spring is a lightweight JEE framework designed to
provide louse coupling between components and a
POJO model.
 Spring provides a Container which manages business
objects and their lifecycle. Dependencies between
various components are supplied via some XML
configurations.
 Spring Container is factory object in memory making is
truly lightweight.

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SPRING CORE MODULE
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 Dependency Injection (IoC - Inversion of Control)
It is a process in which objects define their dependencies,
means , the other objects they work with it.
The container then injects those dependencies when it
creates the bean.
This process is fundamentally the inverse, hence the
name Inversion of Control (IoC).
This is achieved by XML file that specifies which beans
are created and what their properties are.
SPRING CORE MODULE
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 IoC container is an implementation of BeanFactory
interface.
 Extension of above interface is ApplicationContext and
WebApplicationContext interfaces.
 The most commonly used form of IoC container is the
ApplicationContext implementation.
 Container will get configurations from XML files.
SPRING CORE MODULE
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TYPES OF DI
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 Setter injection
 Constructor injection
 Defining a BEAN Objects whose implementations are
likely to change are defined in XML file.
 Use the <bean> tag to define object’s name and class
 Use nested <property> or <constructor-arg> elements
to assign values to the object
TYPES OF DI
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 First create a file called spring.xml and put it in “src”
folder of your project.
 In that case you can instantiate container with more
than one way let’s see it in example “spring-ex1”
 If your bean configuration file is in file system, then use
following methods to Instantiate container.
 BeanFactory factory = new XmlBeanFactory(new
FileSystemResource("spring.xml"));
Spring Basics
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 ApplicationContext context = new
FileSystemXmlApplicationContext("spring.xml");
 If your bean configuration file is in class path, then use
following methods to Instantiate container.
ApplicationContext context = new
ClassPathXmlApplicationContext("spring.xml");
 Subdirectory of class path
ApplicationContext context = new
ClassPathXmlApplicationContext("/beans/spring.xml");
Spring Basics
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 Using with Web Applications
Instantiate container with special listener when app
loads. And access container with static methods in
WebApplicationContextUtils.
 Get instance from the container
YourType yourBean =
(YourType) context.getBean("bean-name");
Spring Basics
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 How to set BEAN properties ?
 <property name="foo" value="bar"/>
When you declare a bean with above syntax
it calls the zero-argument constructor when the object is
instantiated. Use <property…/> tags to specific what
setters are called after the constructor executes.
<bean id="some-name" class="package.SomeClass">
<property name="someProp" value="some-value"/>
</bean>
Spring Basics
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 This means that when getBean() is called, the zero argument
constructor is called, then setXXX is called.
Simple type conversions will be performed, so setXXX can take
String, int, Integer, double, Double, etc.
 <constructor-arg value="…"/>
Instead of calling the zero-arg constructor and then calling setters,
you can supply constructor arguments.
<bean id="some-name" class="package.SomeClass">
<constructor-arg value="some-value"/>
</bean>
Spring Basics
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 What to use to initiate objects property or constructor ?
 There may not even be a zero arg constructor in that
case use <property />.
 Use constructor-arg only for immutable classes that
have no setter methods. Use property otherwise.
Spring Basics
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 <bean factory-method="makeBean">
 Sometimes you don’t know the specific type of bean you will
need. You need to run some logic to determine this.
So, instead of calling constructor, you call a method that returns
an object.
<bean id="some-name" class="package.HelperClass" factory-
method="makeSomeBean">
</bean>
This means that when getBean is called, the static method.

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 HelperClass.makeSomeBean() is invoked (with no arguments),
and the output of that method is the bean.
Note that “class” is not the class of the bean, but it is a helper
class that contains the static factory method.
 You use the “constructor-arg” to supply values to the factory
method
<bean id="some-name" class="package.HelperClass"
factory-method="makeSomeBean">
<constructor-arg value=“Test"/>
</bean>

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 This means that the static method call
HelperClass.makeSomeBean(“Test") determines the
output of getBean().
 Note that no constructor is called directly (although
the static method might use a constructor internally).
So “constructor-arg” is a bad choice of name.
 “class” is not the type of the bean, but the name of the
class that contains the static method.

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 <bean … scope="singleton"> (or no scope)
Every time you call getBean() on the same name, you
get the same instance. Default if no scope specified.
<property…/> and <constructor-arg…/> only invoked
the first time (if bean of that name not already
instantiated)
 You get the same instance per container. If you
reinstantiate the container, then you get new instance
Why it is required?
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 <bean … scope="prototype">
Every time you call getBean, you get new instance
<property> and <constructor-arg> invoked every time
 Other scopes
scope="request" and scope="session“
Available only in Web applications.
 scope="globalSession"
Used only in portal apps.
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Basics of Spring - KNOWARTH

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