设计模式之代理模式

代理模式定义：为其他对象提供一种代理以控制对这个对象的访问。

优点：

1、职责清晰。

2、高扩展性。

3、智能化。

下面分析三种形式的代理。

第一种、简单的代理模式

类图如下：

实现代码如下：

玩家抽象类：

package com.designpatterns.proxy;

public interface IGamePlayer {
	public void login(String name,String password);
	public void killBoss();
	public void upgrade();
}

玩家实现类：

package com.designpatterns.proxy;

public class GamePlayer implements IGamePlayer {
	private String name="";

	public GamePlayer(String name) {
		this.name=name;
	}

	@Override
	public void login(String name, String password) {
		System.out.println("用户名为："+name+"的用户,"+this.name+"登录了！");

	}

	@Override
	public void killBoss() {
		System.out.println(this.name+"正在打怪！");

	}

	@Override
	public void upgrade() {
		System.out.println(this.name+"升一级！");

	}
}

代理实现类：

package com.designpatterns.proxy;

public class GamePlayerProxy implements IGamePlayer {

	private IGamePlayer gamePlayer=null;
	public GamePlayerProxy(IGamePlayer gamePlayer) {
		this.gamePlayer=gamePlayer;
	}

	@Override
	public void login(String name, String password) {
		this.gamePlayer.login(name, password);

	}

	@Override
	public void killBoss() {
		this.gamePlayer.killBoss();

	}

	@Override
	public void upgrade() {
		this.gamePlayer.upgrade();

	}
}

测试类：

package com.designpatterns.proxy;

public class Client {

	public static void main(String[] args) {
		IGamePlayer zs = new GamePlayer("张三");
		IGamePlayer proxy = new GamePlayerProxy(zs);
		proxy.login("zhangsan", "123456");
		proxy.killBoss();
		proxy.upgrade();

	}
}

第二种： 强制代理

这种情况下，必须通过制定的代理，才能访问到处理事件。

类图如下：

实现代码如下：

玩家抽象类;

package com.designpatterns.proxyforced;

public interface IGamePlayer {
	public void login(String name,String password);
	public void killBoss();
	public void upgrade();
	public IGamePlayer getProxy();
}

玩家实现类：

package com.designpatterns.proxyforced;

public class GamePlayer implements IGamePlayer {
	private String name="";
	private IGamePlayer proxy;

	public GamePlayer(String name) {
		this.name=name;
	}

	@Override
	public void login(String name, String password) {
		if (this.isProxy()) {
			System.out.println("用户名为："+name+"的用户,"+this.name+"登录了！");
		}else {
			System.out.println("请使用制定的代理！");
		}
	}

	@Override
	public void killBoss() {
		if (this.isProxy()) {
			System.out.println(this.name+"正在打怪！");
		}else {
			System.out.println("请使用制定的代理！");
		}
	}

	@Override
	public void upgrade() {
		if (this.isProxy()) {
			System.out.println(this.name+"升一级！");
		}else {
			System.out.println("请使用制定的代理！");
		}
	}

	@Override
	public IGamePlayer getProxy() {
		if(this.proxy==null){
			this.proxy=new GamePlayerProxy(this);
		}
		return this.proxy;
	}

	private boolean isProxy(){
		if(this.proxy==null){
			return false;
		}else {
			return true;
		}
	}
}

代理实现类：

package com.designpatterns.proxyforced;

public class GamePlayerProxy implements IGamePlayer {

	private IGamePlayer gamePlayer=null;
	public GamePlayerProxy(IGamePlayer gamePlayer) {
		this.gamePlayer=gamePlayer;
	}

	@Override
	public void login(String name, String password) {
		this.gamePlayer.login(name, password);
	}

	@Override
	public void killBoss() {
		this.gamePlayer.killBoss();
	}

	@Override
	public void upgrade() {
		this.gamePlayer.upgrade();
	}

	@Override
	public IGamePlayer getProxy() {
		return this;
	}
}

测试类：

package com.designpatterns.proxyforced;

public class Client {
	public static void main(String[] args) {
		IGamePlayer zs = new GamePlayer("张三");
		System.out.println("-----------------------------\n错误的用法");
		IGamePlayer proxy = new GamePlayerProxy(zs);
		proxy.login("zhangsan", "123456");
		proxy.killBoss();
		proxy.upgrade();

		System.out.println("-----------------------------\n正确的用法");
		proxy = zs.getProxy();
		proxy.login("zhangsan", "123456");
		proxy.killBoss();
		proxy.upgrade();
	}
}

第三种、 动态代理

动态代理是在实现阶段不用关心代理谁，而在运行阶段才指定代理哪一个对象。（AOP就是典型的例子）

类图如下：

代码实现如下：

抽象的代理对象：

package com.designpatterns.dynamicproxy;

public interface Subject {
	public void sayHello();
	public void sayByeBye();
}

实现的代理对象;

package com.designpatterns.dynamicproxy;

public class RealSubject implements Subject {
	@Override
	public void sayHello() {
		System.out.println("hello!");
	}

	@Override
	public void sayByeBye() {
		System.out.println("ByeBye!");
	}
}

动态代理的Handler类：

package com.designpatterns.dynamicproxy;

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

public class MyInvocationHandler implements InvocationHandler {
	private Object target = null;

	public MyInvocationHandler(Object object) {
		this.target = object;
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		(new Before()).sayBefore();//AOP
		Object o = method.invoke(this.target, args);
		(new After()).sayAfter();//AOP
		return o;
	}
}

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

在这里打断一下，为了体现AOP的编程思想，我们可以在这里实现一个简单的切面编程，我定义了两个方法。然后在动态代理的Handler类中调用。

After类：

package com.designpatterns.dynamicproxy;

public class After {
	public void sayAfter() {
		System.out.println("I am after!");
	}
}

Before类：

package com.designpatterns.dynamicproxy;

public class Before {
	public void sayBefore() {
		System.out.println("I am before!");
	}
}

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

动态代理类：

package com.designpatterns.dynamicproxy;

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

public class SubjectDynamicProxy<T> {
	@SuppressWarnings("unchecked")
	public static <T> T newProxyInstance(Object O) {
		ClassLoader loader = O.getClass().getClassLoader();
		Class<?>[] interfaces = O.getClass().getInterfaces();
		InvocationHandler h = new MyInvocationHandler(O);
		return (T) Proxy.newProxyInstance(loader, interfaces, h);
	}
}

测试类：

package com.designpatterns.dynamicproxy;


public class Client {

	public static void main(String[] args) {
		RealSubject realSubject= new RealSubject();
		Subject subjectProxy= SubjectDynamicProxy.newProxyInstance(realSubject);
		subjectProxy.sayHello();
		subjectProxy.sayByeBye();
		}
}

以上就是三种形式的代理模式。

参考资料：
设计模式之禅

备注：
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http://blog.youkuaiyun.com/wsyw126/article/details/51313972
by WSYW126