代理是基本的设计模式之一它为你提供额外的或不同的操作,而插入的用来代替"实际"对象的对象.

package typeinfo;
//: typeinfo/SimpleProxyDemo.java
import static net.mindview.util.Print.*;

interface Interface {
  void doSomething();
  void somethingElse(String arg);
}

class RealObject implements Interface {
  public void doSomething() { print("doSomething"); }
  public void somethingElse(String arg) {
    print("somethingElse " + arg);
  }
}    

class SimpleProxy implements Interface {
  private Interface proxied;
  public SimpleProxy(Interface proxied) {
    this.proxied = proxied;
  }
  public void doSomething() {
    print("SimpleProxy doSomething");
    proxied.doSomething();
  }
  public void somethingElse(String arg) {
    print("SimpleProxy somethingElse " + arg);
    proxied.somethingElse(arg);
  }
}    

class SimpleProxyDemo {
  public static void consumer(Interface iface) {
    iface.doSomething();
    iface.somethingElse("bonobo");
  }
  public static void main(String[] args) {
    consumer(new RealObject());
    consumer(new SimpleProxy(new RealObject()));
  }
} /* Output:
doSomething
somethingElse bonobo
SimpleProxy doSomething
doSomething
SimpleProxy somethingElse bonobo
somethingElse bonobo
*///:~

动态代理的思想更向前迈进了一步,因为它可以动态地创建代理并动态地处理对所代理方法的调用.

package typeinfo;
//: typeinfo/SimpleDynamicProxy.java
import java.lang.reflect.*;

class DynamicProxyHandler implements InvocationHandler {
  private Object proxied;
  public DynamicProxyHandler(Object proxied) {
    this.proxied = proxied;
  }
  public Object
  invoke(Object proxy, Method method, Object[] args)
  throws Throwable {
    System.out.println("**** proxy: " + proxy.getClass() +
      ", method: " + method + ", args: " + args);
    if(args != null)
      for(Object arg : args)
        System.out.println("  " + arg);
    return method.invoke(proxied, args);
  }
}    

class SimpleDynamicProxy {
  public static void consumer(Interface iface) {
    iface.doSomething();
    iface.somethingElse("bonobo");
  }
  public static void main(String[] args) {
    RealObject real = new RealObject();
    consumer(real);
    // Insert a proxy and call again:
    Interface proxy = (Interface)Proxy.newProxyInstance(
      Interface.class.getClassLoader(),
      new Class[]{ Interface.class },
      new DynamicProxyHandler(real));
    consumer(proxy);
  }
} /* Output: (95% match)    
doSomething
somethingElse bonobo
**** proxy: class $Proxy0, method: public abstract void Interface.doSomething(), args: null
doSomething
**** proxy: class $Proxy0, method: public abstract void Interface.somethingElse(java.lang.String), args: [Ljava.lang.Object;@42e816
  bonobo
somethingElse bonobo
*///:~