Monday, May 22, 2017

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. As we 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 scope of the bean is one of those details. This Spring tutorial is next on my earlier post on Spring like how to implement LDAP authentication using Spring Security and  How to limit the number of user sessions in a web application, if you haven’t read them already you may find them useful.


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.



bean scope in Spring 2.5 and spring 3.0Singleton 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 is 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.


Further Reading
Spring Framework 5: Beginner to Guru
Spring Master Class - Beginner to Expert
Introduction to Spring MVC 4 By Bryan Hansen
Spring and Hibernate for Beginners


Other Java tutorials you may like

References

P.S. - If you want to learn how to develop RESTful Web Service using Spring MVC in-depth, I suggest you join the REST with Spring certification class by Eugen Paraschiv. One of the best courses to learn REST with Spring MVC. 

4 comments :

Jirka Pinkas said...

Or since Spring 3.0 you can use standard annotations JSR-330 (known as @Inject), that were introduced in Java EE 6. There's also annotation @Scope, but singleton is defined using annotation @Singleton.

kim said...

What is default bean Scope in Spring 3.0? Singleton scope ?? Is there any way we can change default bean Scope to prototype or request ?

Anonymous said...

i want to know how can i restrict the no of bean objects to be created for a spring bean to 50.

Agashi24 said...

Hi....

Thanks for your awesome tutorials, gained lot of information!!
I was asked in an interview, we know that the default bean scope in Spring is Singleton, why is it so?
i am totally stuck, not able to find why, can you please help me?

TIA

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