Spring - How can I destroy my prototype-scoped beans?

Question

I've got a singleton bean that has a method that creates instances of a prototype bean. I'm using the method documented here to get instances of the prototype bean.

public class SingletonService implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    public void go() {

        MyPrototypeBean prototype = applicationContext
            .getBean(MyPrototypeBean.class);

        prototype.doSomething();
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
        throws BeansException {

        this.applicationContext = applicationContext;
    }
}

At first I thought that this was good enough, that my instance of 'prototype' would go out of scope when the 'go' method returned, meaning that the instance would have not reference and would be garbage collected.

However, a peer pointed out the following statement from the documentation:

The client code must clean up prototype-scoped objects and release expensive resources that the prototype bean(s) are holding.

So it sounds like Spring will retain a reference, and so the gc will never pick it up? If that's the case how do I tell Spring to release the reference? The documentation mentions that I can use a 'custom bean post-processor', but it's not clear where that processor would fit in and what code it would run.

Thanks all in advance for helping out, Roy

Answer 1

I think you're misunderstanding the documentation. It's just saying Spring won't manage the lifecycle of the prototype bean, so @PreDestroy (etc.) methods need to be called by your own code. Spring won't retain a reference.