Spring-单例bean内的原型bean

Question

Spring has bean types/scopes like
-singleton bean (only one bean per application context)
-prototype bean (a new bean per request)

Now if there is a reference to prototype bean inside a singleton bean, is there a way to get a new prototype bean (which is inside the singleton bean) on every request to the singleton bean.
If yes, what would the configurations look like?

Answer 1

There is a way with lookup-method like this:

import org.springframework.beans.factory.annotation.Lookup;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

public final class Main {

    public static void main(String[] args) {
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(Config.class);
        for (int i = 0; i < 10; i++) {
            System.out.println(i + ".- call: " + applicationContext.getBean(Singleton.class));
        }
    }

    @ComponentScan("foo")
    @Configuration
    public static class Config {

    // It's important to define SingletonBase component with @Component annotation and not here, If you define SingletonBase initialization here, It'll not work!

        @Bean
        @Scope(BeanDefinition.SCOPE_PROTOTYPE)
        public Prototype prototype() {
            return new PrototypeBase();
        }
    }

    public interface Prototype {

        public long getInstanceId();
    }

    public interface Singleton {

        public Prototype getPrototype();
    }

    // It's important define SingletonBase component as this, If you define SingletonBase initialization inside a factory it'll not work!
    @Component
    public static class SingletonBase implements Singleton {

        private static long instanceIdGenerator = 1L;
        private long instanceId = generateId();

        private static synchronized long generateId() {
            return instanceIdGenerator++;
        }

        public SingletonBase() {
            System.out.println("Singleton initialized!");
        }

        @Override
        public String toString() {
            return "SingletonBase{" + "instanceId=" + instanceId + ", prototypeId=" + getPrototype().getInstanceId() + '}';
        }

        @Override
        @Lookup
        public Prototype getPrototype() {
            return null;
        }
    }

    public static class PrototypeBase implements Prototype {

        private static long instanceIdGenerator = 1L;
        private long instanceId = generateId();

        private static synchronized long generateId() {
            return instanceIdGenerator++;
        }

        public PrototypeBase() {
            System.out.println("Prototype initialized!");
        }

        public long getInstanceId() {
            return instanceId;
        }
    }
}

It prints:

Singleton initialized!
Prototype initialized!
0.- call: SingletonBase{instanceId=1, prototypeId=1}
Prototype initialized!
1.- call: SingletonBase{instanceId=1, prototypeId=2}
Prototype initialized!
2.- call: SingletonBase{instanceId=1, prototypeId=3}
Prototype initialized!
3.- call: SingletonBase{instanceId=1, prototypeId=4}
Prototype initialized!
4.- call: SingletonBase{instanceId=1, prototypeId=5}
Prototype initialized!
5.- call: SingletonBase{instanceId=1, prototypeId=6}
Prototype initialized!
6.- call: SingletonBase{instanceId=1, prototypeId=7}
Prototype initialized!
7.- call: SingletonBase{instanceId=1, prototypeId=8}
Prototype initialized!
8.- call: SingletonBase{instanceId=1, prototypeId=9}
Prototype initialized!
9.- call: SingletonBase{instanceId=1, prototypeId=10}   

Answer 2

Inject the ApplicationContext in the singleton bean and use the getBean method to get the prototype.

@Autowired
private ApplicationContext ctx;

public void request() {
    MyProptotypeBean mpb = this.ctx.getBean(MyProptotypeBean.class);//new instance for evety call to the method
}