Bean scope in Spring framework or Spring MVC are scope for a bean managed by Spring IOC container. As we know that Spring is a framework which 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 Spring framework. Spring allows you to define how those beans will be created and scope of 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 number of user session in 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
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.
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 Singleton pattern in Java where only one instance of bean is created per Spring container. So no matter how many times you call getBean() method, same bean instance will be returned if its bean scope is declared as Singleton. While in case of prototype bean scope, every getBean() call creates a new instance of Spring bean. 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 bean created and supplied by Spring framework, while Session bean scope allows Web application to have bean instance per session basis. both of these bean scope are available on WebApplicationContext or any web aware application context. Last one which is global session bean scope is only applicable on portlet aware bean scope and allows bean instance per global session. In short Singleton vs prototype is an important which clearly segregate 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
Since singleton is also default scope in spring framework, following declaration is exactly same and creates bean on singleton scope.
Though I prefer explicit declaration to make bean scope loud and clear. Now every time you call getBean("auditService") it will return same instance of AuditService.
AuditService auditService = ApplicationContext.getBean("auditService");
//bean configured on prototype bean scope
In case of prototype beans cope every call to getBean("auditServie") will return different instance 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
Bean Scope in Spring 2.5 and Spring 3.0 is similar, all default scopes are still supported in spring 3.0 with addition of few new scopes like thread scope or SimpleThreadScope which is a scope backed by thread. You can also register your own custom scope using CustomScopeConfigurer utility., there is no new scope for bean is introduced on spring 3.0
That’s about what is bean scope in Spring framework. Since bean creation is managed by Spring IOC container its worth remember that how to specify 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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