Implementing class target method exception using proxy object execution

使用JDKway when creating a dynamic proxy object,Usually it will be cast to the target interface type.

public class Test {
    

    public static void main(String[] args) throws Exception{
    

        BaseController baseController = new BaseControllerImpl();
        InvocationHandler handler = new MyInvocationHandler(baseController);
        BaseController target = (BaseController) Proxy.newProxyInstance(BaseController.class.getClassLoader(), new Class[]{
    BaseController.class}, handler);
        target.a4("111");

    }

}

此时的target就是一个代理对象,同时是Proxy与BaseController的实例,At this time, it is possible to call the method of the interface when the method is called in the form of an interface,什么意思？ 可参考如下代码

    public static void main(String[] args)throws Exception {
    
        Method a4 = BaseController.class.getMethod("a4", String.class);

        Method a4Impl = BaseControllerImpl.class.getMethod("a4", String.class);

        BaseControllerImpl baseController = new BaseControllerImpl();

        a4Impl.invoke(baseController,"111");
        a4.invoke(baseController,"222");

    }

BaseController是接口,BaseControllerImpl 是实现类,got the interfacea4method and implementation typea4方法,然后创建了BaseController的一个实现类,Use the implementation class to invoke the two reflections separatelymethod,The call was found to be successful.

However, if the created proxy object is used to execute the method of the implementation class, an exception will be thrown.

    public static void main(String[] args) throws Exception{
    

        BaseController baseController = new BaseControllerImpl();
        InvocationHandler handler = new MyInvocationHandler(baseController);
        BaseController target = (BaseController) Proxy.newProxyInstance(BaseController.class.getClassLoader(), new Class[]{
    BaseController.class}, handler);
        Method a4 = BaseController.class.getMethod("a4", String.class);
        Method a4Impl = BaseControllerImpl.class.getMethod("a4", String.class);
        a4.invoke(target,"111");
        a4Impl.invoke(target,"222");

    }

This can actually be well understoodtarget是一个代理对象,是BaseController的代理对象,本身和BaseControllerImpl是没有关系的,They both achieved itBaseController接口,So it can be said to be a sibling relationship,However, the same method calls cannot be implemented between brothers,It must be the parent class or its own method.所以在JDKin the implemented proxy,When calling the interface target method,is a method of the interface to call.

可通过debugSee when the method is called on the proxy objectmethod签名,It is obvious that it is the method signature in the interface.对于SpringIn terms of the aspect declared in ,Aspect classes do not generate proxy objects,Just notificationSpringConfigured according to the aspectpointcut来检测bean是否需要创建代理对象,In which way to create etc,The method declared by the aspect class is only used to tellSpringWhich notification type it is.