动态代理小模拟总是找不到错误！小菜

document 一：

public interface Subject {
public void doAction();
}

document 二：

import com.staticproxy.Subject;

public class RealSubject implements Subject {

@Override
public void doAction() {
System.out.println("From RealSubject!");
}

}

document 三：

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyProxy implements InvocationHandler {
private Object object;

public MyProxy(Object object) {
super();
this.object = object;
}

//通过动态代理，将调用方法转给 InvocationHandler 类型的 handler.
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
this.before();
method.invoke(object, args);
this.after();
return null;
}

private void before() { //额外增加的
System.out.println("Before doing");
}

private void after() { //额外增加的.
System.out.println("After doing");
}

}
document 四：

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

public class Client {
public static void main(String[] args) throws Exception {
RealSubject realSubject = new RealSubject(); // 真实角色.

InvocationHandler handler = new MyProxy(realSubject);
// 为了生成 DynamicProxy.

Class<?> classType = handler.getClass();

// 下面的代码一次性生成代理

Subject subject = (Subject) Proxy.newProxyInstance(classType
.getClassLoader(), realSubject.getClass().getInterfaces(),
handler);

subject.doAction();

}

}
为什么总是 ：
Exception in thread "main" java.lang.ClassCastException: $Proxy0 cannot be cast to com.dynamicproxy.Subject
找不到哪里错，应该是对的，崩溃。
[解决办法]

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyProxy implements InvocationHandler {
private Object object;

public MyProxy(Object object) {
super();
this.object = object;
}

//通过动态代理，将调用方法转给 InvocationHandler 类型的 handler.
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
this.before();
method.invoke(object, args);
this.after();
return null;
}

private void before() { //额外增加的
System.out.println("Before doing");
}

private void after() { //额外增加的.
System.out.println("After doing");
}

}

这一部分首先有问题，大概应该这样：

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyProxy implements InvocationHandler {

//通过动态代理，将调用方法转给 InvocationHandler 类型的 handler.
@Override
public Object invoke(Object proxy, Method method, Object[] args) 
 
throws Throwable {
this.before();
Object result = method.invoke(proxy, args);
this.after();
return result;
}

private void before() { //额外增加的
System.out.println("Before doing");
}

private void after() { //额外增加的.
System.out.println("After doing");
}

}

然后下面这一句：

Subject subject = (Subject) Proxy.newProxyInstance(classType
.getClassLoader(), realSubject.getClass().getInterfaces(),
handler);

改成这样试试：

Subject subject = (Subject) Proxy.newProxyInstance(
  realSubject.getClass().getClassLoader(), 
  new Class<?>[]{ Subject.class },
  new MyProxy()
);

[解决办法]

引用:

引用:Java code?123456789101112131415161718192021222324252627282930import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method; public class MyProxy implement……

恩，试了一下，我刚刚说的的确不对……
下面这个可以：

public interface Subject {

  public void doAction();
}

public class RealSubject implements Subject {

  @Override
  public void doAction() {
    
    System.out.println("From RealSubject!");
  }
}

public class MyProxy implements InvocationHandler {
  
  private Object o;
  MyProxy(Object o) {
    
    this.o = o;
  }
  
  @Override
  public Object invoke(Object proxy, Method method, Object[] args)
          throws Throwable {
    
    before();
    Object result = method.invoke(o, args);
    after();
    return result;
  }

  private void before() {
    
    System.out.println("Before doing");
  }

  private void after() {
    
    System.out.println("After doing");
  }
}

public class Client {

  public static void main(String[] args) throws Exception {
    
    RealSubject realSubject = new RealSubject(); 

    Subject subject = (Subject)Proxy.newProxyInstance(
            
            realSubject.getClass().getClassLoader(), 
            new Class<?>[]{ Subject.class },
            new MyProxy(realSubject)
    );
    subject.doAction();
  } 
 
}

[解决办法]
楼主的代码没有问题