详解Spring中Lookup注解的使用

	/**
	 * 1、判断是不是独立的类，非静态内部类则无法生成bean,
	 * 2、判断是不是接口或者抽象类（有一种特殊情况），是则无法生成
	 * 3、判断如果是抽象类，但是里面有某个方法上面加油@lookup注解，则也可以生成bean
	 * Determine whether the given bean definition qualifies as candidate.
	 * <p>The default implementation checks whether the class is not an interface
	 * and not dependent on an enclosing class.
	 * <p>Can be overridden in subclasses.
	 * @param beanDefinition the bean definition to check
	 * @return whether the bean definition qualifies as a candidate component
	 */
	protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
		AnnotationMetadata metadata = beanDefinition.getMetadata();
		return (metadata.isIndependent() && (metadata.isConcrete() ||
				(metadata.isAbstract() && metadata.hasAnnotatedMethods(Lookup.class.getName()))));
	}

@Component
public abstract class C1 {
 
}

@Component
public abstract class C1 {
 
    @Lookup
    public void a(){}
}

@Component
public class D3 {
 
    @Autowired
    private E4 e4;
 
    public void a(){
        System.out.println(this.e4);
    }
}
 
@Component
public class E4 {
}

@Component
public class D3 {
 
    public void a(){
        System.out.println(this.a1());
    }
 
    @Lookup
    public E4 a1(){
        return null;
    }
}