Spring Prototype scoped bean in a singleton

Question

I am trying to inject a prototype bean in a singleton bean such that every new call to a singleton bean method has a new instance of the prototype bean.

Consider a singleton bean as below:

    @Component     public class SingletonBean {        @Autowired         private PrototypeBean prototypeBean;         public void doSomething() {          prototypeBean.setX(1);          prototypeBean.display();        }     } 

I expect that every time the doSomething() method is called, a new PrototypeBean instance is utilized.

Below is the prototype bean:

     @Component       @Scope(value="prototype", proxyMode = ScopedProxyMode.TARGET_CLASS)      public class PrototypeBean {         Integer x;          void setX(Integer x) {          this.x = x;         }          void display() {           System.out.println(x);         }     } 

What seems to be happening is that spring is being overeager in handing over a new instance of PrototypeBean in the doSomething() method. That is, the 2 lines of code in the doSomething() method are creating a new instance of prototypeBean in each line.

And so in the 2nd line - prototypeBean.display() prints NULL.

What is missing in configuration for this injection?

Answer 1

From Spring documentation:

You do not need to use the <aop:scoped-proxy/> in conjunction with beans that are scoped as singletons or prototypes. If you try to create a scoped proxy for a singleton bean, the BeanCreationException is raised.

It seems the documentation has changed a bit for version 3.2 documentation where you can find this sentence:

You do not need to use the <aop:scoped-proxy/> in conjunction with beans that are scoped as singletons or prototypes.

It seems that its not expected you use a proxied prototype bean, as each time it is requested to the BeanFactory it will create a new instance of it.

---

In order to have a kind of factory for your prototype bean you could use an ObjectFactory as follows:

@Component public class SingletonBean {      @Autowired     private ObjectFactory<PrototypeBean> prototypeFactory;      public void doSomething() {         PrototypeBean prototypeBean = prototypeFactory.getObject();         prototypeBean.setX(1);         prototypeBean.display();     } } 

and your prototype bean would be declared as follows:

@Component  @Scope(value="prototype") public class PrototypeBean {     // ... }