//接口（动态代理只能代理接口）
public interface Subject {  public void request();
}  

//接口实现 ：实现了Subject的request()方法
public class RealSubject implements Subject{  public void request(){  System.out.println("From real subject.");  }
} 

Inb

//实现了InvocationHandler  接口
public class DynamicSubject implements InvocationHandler
{  private Object obj;//这是动态代理的好处，被封装的对象是Object类型，接受任意类型的对象  public DynamicSubject()  {  }  public DynamicSubject(Object obj)  {  this.obj = obj;  }  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable  {  System.out.println("before calling " + method);  method.invoke(obj, args);  System.out.println("after calling " + method);  return null;  }  }  

public class Client {  public static void main(String[] args) throws Throwable{  // TODO Auto-generated method stub  Subject rs=new RealSubject();//这里指定被代理类  InvocationHandler ds=new DynamicSubject(rs);  Class<?> cls=rs.getClass();  //生成代理类  ，注意subject是Proxy的子类并且实现了Subject接口的一个类。Subject subject=(Subject) Proxy.newProxyInstance(  cls.getClassLoader(),cls.getInterfaces(), ds);       

}

以上就是动态代理的使用方法，有一点很奇怪，那就是invoke方法是如何被调用的呢？ 可以看到在以上代码中并没有invoke的身影，那是因为有关invoke的调用时在Proxy类中，invoke方法并不是给我们显示的调用，查看源码我们可以看到。

首先看Proxy的静态方法newProxyInstance()

public static Object newProxyInstance(ClassLoader loader,  Class<?>[] interfaces,  InvocationHandler h)
throws IllegalArgumentException
{  if (h == null) {  throw new NullPointerException();  }  /* * Look up or generate the designated proxy class. */  Class cl = getProxyClass(loader, interfaces);  /* * Invoke its constructor with the designated invocation handler. */  try {  /* * Proxy源码开始有这样的定义： * private final static Class[] constructorParams = { InvocationHandler.class }; * cons即是形参为InvocationHandler类型的构造方法 */  Constructor cons = cl.getConstructor(constructorParams);  return (Object) cons.newInstance(new Object[] { h });    //此处返回.} catch (NoSuchMethodException e) {  throw new InternalError(e.toString());  } catch (IllegalAccessException e) {  throw new InternalError(e.toString());  } catch (InstantiationException e) {  throw new InternalError(e.toString());  } catch (InvocationTargetException e) {  throw new InternalError(e.toString());  }
}  

这个方法实际是利用反射，返回了一个Proxy的子类，实现了指定的接口，返回的类叫做$Proxy0, 这个类包含了invoke的秘密！ 请看源码：

public final class $Proxy0 extends Proxy implements Subject {  private static Method m1;  private static Method m0;  private static Method m3;  private static Method m2;  static {  try {  m1 = Class.forName("java.lang.Object").getMethod("equals",  new Class[] { Class.forName("java.lang.Object") });  m0 = Class.forName("java.lang.Object").getMethod("hashCode",  new Class[0]);  m3 = Class.forName("***.RealSubject").getMethod("request",  new Class[0]);  m2 = Class.forName("java.lang.Object").getMethod("toString",  new Class[0]);  } catch (NoSuchMethodException nosuchmethodexception) {  throw new NoSuchMethodError(nosuchmethodexception.getMessage());  } catch (ClassNotFoundException classnotfoundexception) {  throw new NoClassDefFoundError(classnotfoundexception.getMessage());  }  } //static  public $Proxy0(InvocationHandler invocationhandler) {  super(invocationhandler);  }  @Override  public final boolean equals(Object obj) {  try {  return ((Boolean) super.h.invoke(this, m1, new Object[] { obj })) .booleanValue();  } catch (Throwable throwable) {  throw new UndeclaredThrowableException(throwable);  }  }  @Override  public final int hashCode() {  try {  return ((Integer) super.h.invoke(this, m0, null)).intValue();  } catch (Throwable throwable) {  throw new UndeclaredThrowableException(throwable);  }  }  public final void request() {  try {  super.h.invoke(this, m3, null);  return;  } catch (Error e) {  } catch (Throwable throwable) {  throw new UndeclaredThrowableException(throwable);  }  }  @Override  public final String toString() {  try {  return (String) super.h.invoke(this, m2, null);  } catch (Throwable throwable) {  throw new UndeclaredThrowableException(throwable);  }  }
}

该类中利用反射获取到了4个方法，Object类自带的equals，hasCode,toString ,以及接口Subject的唯一方法request，因此当我们在主函数中调用request.xxx(方法名),就是在$Proxy0类中调用相应方法，每个方法中都有 super.h.invoke(this,m3,null);        invoke函数在此起到了作用！