Spring @PreDestroy method

Question

I found out that @PreDestroy only work with singleton scoped bean. I was thinking what could go wrong if we use it with prototype scoped bean. Anything at all??? I dont think so. I think this is just not implemented in spring as they would have to keep the references to all the beans created. Tell me if i am wrong

Answer 1

Spring can only initialize/destroy beans it also controllers and basically prototype scoped beans aren't under the control of spring (after construction). It doesn't know when it is cleaned up, destroyed or what so ever. As such the @PreDestroy method isn't callable for prototype beans (as they do not have a clearly defined lifecycle like singletons or request scoped beans).

Answer 2

The @PreDestroy annotation does not belong to Spring, it’s located in the jsr250-api library jar under javax.annotation package.

By default, Spring will not aware of the @PreDestroy annotation. To enable it, you have to either register CommonAnnotationBeanPostProcessor or specify the <context:annotation-config /> in bean XML configuration file.

Answer 3

For "prototype" scoped beans, Spring does not call the @PreDestroy method.

Here is the answer from the Spring reference manual. Section 7.5.2

http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#beans-factory-scopes-prototype

In contrast to the other scopes, Spring does not manage the complete lifecycle of a prototype bean: the container instantiates, configures, and otherwise assembles a prototype object, and hands it to the client, with no further record of that prototype instance.

Thus, although initialization lifecycle callback methods are called on all objects regardless of scope, in the case of prototypes, configured destruction lifecycle callbacks are not called. The client code must clean up prototype-scoped objects and release expensive resources that the prototype bean(s) are holding.

To get the Spring container to release resources held by prototype-scoped beans, try using a custom bean post-processor, which holds a reference to beans that need to be cleaned up.