The method of injecting multiple instances into a single instance in Spring

There will be problems in injecting Spring's prototype into singleton. For details, see

The useless solution of Spring Bean's prototype

In addition to the methods introduced in this article (ApplicationContext.getBean and proxy mode), there are other implementations in the java (Spring) world.

Let's talk about it here.

 

1. Using Spring's ObjectFactory

If the original code is like this

    @Autowired
    private PrototypeBean bean;

 If it is used directly in a single instance or obtained multiple times in multiple instances, the same instance will be obtained.

Our state bean is invalid.

can be changed to this

    @Autowired
    private ObjectFactory<PrototypeBean> bean;

 Call the getObject method when using

bean.getObject()

 That's it.

 

2. Using Provider<T> proposed by Java's JSR 330

To introduce the jar package javax.inject

import javax.inject.Provider;

  The usage is similar to the previous ObjectFactory, except that the method name becomes get

 

In my opinion, the difference between Provider and ObjectFactory is the difference between Resource and Autowire.

 

 

3. Use Spring's Lookup annotation

import org.springframework.beans.factory.annotation.Lookup;
import org.springframework.stereotype.Component;

@Component
public class MySingletonBean {

    public void showMessage(){
        MyPrototypeBean bean = getPrototypeBean();
      //do your own logic
    }

    @Lookup
    public MyPrototypeBean getPrototypeBean(){
        //spring will override this method by itself
        return null;
    }
}

 This way you don't need to inject a property, but add a method that returns null.