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What is Bean scope in Spring MVC framework with Example

Bean scope in Spring framework or Spring MVC is scope for a bean managed by Spring IOC container. You may know that Spring is a framework that is based on Dependency Injection and Inversion of Control and provides bean management facilities to Java application. In Spring-managed environment bean (Java Classes) are created and wired by the Spring framework. Spring allows you to define how those beans will be created and the scope of the bean is one of those details. 

In spring framework bean declared in ApplicationContext.xml can reside in five scopes:

1) Singleton (default scope)

2) prototype

3) request

4) session

5) global-session

Singleton and prototype are two common bean scope which is available on all Spring Application Context while request, session, and global session bean scope are only available on Web aware application Context like WebApplicationContext.

Now, let’s understand both singleton and prototype bean scope in more detail. 

5 Bean scope in Spring framework with Example

Singleton bean scope is default scope for bean declared in Spring and applicable when you don’t specify scope attribute while specifying bean details in ApplicationContext.xml or Spring configuration file. Singleton bean scope is like a Singleton pattern in Java where only one instance of the bean is created per Spring container. 

So no matter how many times you call getBean() method, the same bean instance will be returned if its bean scope is declared as Singleton. While in the case of prototype bean scope, every getBean() call creates a new instance of Spring bean. The difference between Singleton and prototype bean scope is also a popular Spring question.

On the other hand request, bean scope allows each HTTP request to have its own instance of a bean created and supplied by Spring framework, while Session bean scope allows a Web application to have bean instance per session basis. both of these bean scopes are available on WebApplicationContext or any web-aware application context.

The Last one which is global session bean scope is only applicable to portlet aware bean scope and allows bean instance per global session. In short singleton vs prototype is important which clearly segregates one instance to multiple instances of bean. 

How to specify Bean Scope in Spring Framework

In order to specify bean scope, you can either use Annotation on Spring or you can define it on Application Context, for example in below Spring configuration file AuditService is configured as Singleton using singleton bean scope and PaymentService as prototype bean scope.

//bean configured on singleton bean scope
<bean id="auditService" class="com.sample.service.impl.AuditServiceImpl"  scope="singleton"/>

Since singleton is also default scope in the spring framework, the following declaration is exactly the same and creates bean on singleton scope.

<bean id="auditService" class="com.sample.service.impl.AuditServiceImpl" />

Though I prefer explicit declaration to make bean scope loud and clear. Now every time you call getBean(“auditService“) it will return the same instance of AuditService.

AuditService auditService = ApplicationContext.getBean("auditService");
//bean configured on prototype bean scope
<bean id="auditService" class="com.sample.service.impl.AuditServiceImpl"  scope="prototype"/>

In the case of the prototype, beans cope every call to getBean("auditServie") will return different instances of AuditServiceImpl class. If you want to use Annotation to define bean scope than you can use @Scope("singleton") or @Scope("prototype") on Bean class. 

You will also need to enable component scanning in Order to let Spring knows about bean scope. which you can do it spring 2.5 as <context:component-scan base-package="com.sample.service.impl" />.
Bean scope has not been changed from various spring version and so far two most used spring version spring 2.5 and spring 3.0 has only five bean scope.

Bean Scope in Spring 2.5 and Spring 3.0 is similar, all default scopes are still supported in spring 3.0 with the addition of few new scopes like thread scope or SimpleThreadScope  which is a scope backed by a thread. You can also register your own custom scope using CustomScopeConfigurer utility., there is no new scope for the bean is introduced on spring 3.0

That’s about what is bean scope in the Spring framework. Since bean creation is managed by Spring IOC container its worth remember that how to specify a scope for a particular Bean and what is default scope of Bean which is Singleton to avoid any assumption and code accordingly.

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Published on Java Code Geeks with permission by Javin Paul, partner at our JCG program. See the original article here: What is Bean scope in Spring MVC framework with Example

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