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Tuesday, October 22, 2013

Spring Bean

The objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML <bean/> definitions.

 

The bean definition contains the information called configuration metadata which is needed for the container to know the followings:

  • How to create a bean
  • Bean's lifecycle details
  • Bean's dependencies

 

When defining a <bean> in Spring, you have the option of declaring a scope for that bean. For example, to force Spring to produce a new bean instance each time one is needed, you should declare the bean's scope attribute to be prototype. Similar way if you want Spring to return the same bean instance each time one is needed, you should declare the bean's scope attribute to be singleton.

 

The Spring Framework supports following five scopes, three of which are available only if you use a web-aware ApplicationContext.

  • singleton: This scopes the bean definition to a single instance per Spring IoC container.
  • prototype: This scopes a single bean definition to have any number of object instances.
  • request: This scopes a bean definition to an HTTP request. Only valid in the context of a web-aware Spring ApplicationContext.
  • session: This scopes a bean definition to an HTTP session. Only valid in the context of a web-aware Spring ApplicationContext.
  • global-session: This scopes a bean definition to a global HTTP session. Only valid in the context of a web-aware Spring ApplicationContext.

The default scope of bean is Singleton for Spring framework and No, singleton beans are not thread-safe in Spring framework.

 

Inner beans in Spring

A <bean/> element inside the <property/> or <constructor-arg/> elements defines a so-called inner bean. An inner bean definition does not require a defined id or name; the container ignores these values. It also ignores the scope flag. Inner beans are always anonymous and they are always scoped as prototypes.

 

To add a bean in spring application

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

<bean id="helloWorld" class="com.jeetu.HelloWorld">
<property name="message" value="Hello World!"/>
</bean>

</beans>

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