设计模式--Proxy(代理模式)

http://www.cnblogs.com/itTeacher/archive/2012/12/14/2818572.html

为另一个对象提供一个替身或占位符以控制对这个对象的访问，简而言之就是用一个对象来代表另一个对象。

简单例子：有个接口Italk,people对象实现这个接口的talk()方法，有些想另外加入sing()方法，所以增加代理类talkProxy，实现两个方法.

public interface ITalk
{
    public void talk(String msg);
}

public class People implements ITalk
{
    @Override
    public void talk(final String msg)
    {
        System.out.println(msg);
    }
}

public class TalkProxy implements ITalk
{
    ITalk italk;

    public TalkProxy(final ITalk italk)
    {
        this.italk = italk;
    }

    @Override
    public void talk(final String msg)
    {
        this.italk.talk(msg);
    }

    public void sing(final String songName)
    {
        System.out.println("Song Name:" + songName);
    }
}

public class Client {
	public static void main(final String[] args) {
		final People people = new People();
		people.talk("I can't sing");

		final TalkProxy proxy = new TalkProxy(people);
		proxy.talk("I can talk");
		proxy.sing("I can sing");
	}
}

结果：
I can't sing
I can talk
Song Name:I can sing

常见的代理:
1. 远程代理(Remote Proxy)：为一个位于不同的地址空间的对象提供一个本地的代理对象。这个不同的地址空间可以是在同一台主机中，也
可是在另一台主机中，远程代理又叫做大使(Ambassador)。

import java.rmi.Remote;
import java.rmi.RemoteException;
public interface MyRemote extends Remote {
	public String getUserName(String userId) throws RemoteException;
}

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class MyRemoteImp extends UnicastRemoteObject implements MyRemote {
	protected MyRemoteImp() throws RemoteException {

	}

	public String getUserName(String userId) throws RemoteException {
		return userId + "/myName is Cherry";
	}
}

在cmd中输入： javac MyRemote.java javac MyRemoteImp.java 回车

rmic MyRemoteImp 回车

生成类的class文件及MyRemoteImp_Stub.class文件

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.RemoteException;

public class MyRemoteServer {
	public static void main(final String[] args) {
		// YTODO Auto-generated method stub
		MyRemote remote;
		try {
			remote = new MyRemoteImp();
			Naming.rebind("RemoteService", remote);
		} catch (final RemoteException e) {
			// YTODO Auto-generated catch block
			e.printStackTrace();
		} catch (final MalformedURLException e) {
			// YTODO Auto-generated catch block
			e.printStackTrace();
		}

	}

}

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;

public class MyRemoteClient {
	public static void main(final String[] args) {
		try {
			final MyRemote service = (MyRemote) Naming.lookup("rmi://127.0.0.1/RemoteService");
			final String name = service.getUserName("my id is 001");
			System.out.println(name);
		} catch (final MalformedURLException e) {
			e.printStackTrace();
		} catch (final RemoteException e) {
			e.printStackTrace();
		} catch (final NotBoundException e) {
			e.printStackTrace();
		}
	}

}

打开cmd窗口输入：

start rmiregistry 回车 

javac MyRemoteServer.java 回车

java MyRemoteServer 回车

另开一cmd窗口：

javac MyRemoteClient.java 回车

java MyRemoteClient 回车

输出结果：my id is 001/myName is Cherry

2. 虚拟代理(Virtual Proxy)：根据需要创建开销很大的对象。如果需要创建一个资源消耗较大的对象，先创建一个消耗相对较小的对象来表
示，真实对象只会在需要时才会被真正创建。

public interface Image {
	public void show();
}

public class BigImage implements Image {
	public BigImage() {
		// Thread.sleep(3000);//for simulating to load the big images
		System.out.println("create the big images");
	}

	@Override
	public void show() {
		System.out.println("show the big images");
	}
}

public class ImageProxy implements Image {
	Image image;

	public ImageProxy() {

	}

	public ImageProxy(final Image image) {
		this.image = image;
	}

	@Override
	public void show() {
		if (this.image == null) {
			this.image = new BigImage();
		}
		this.image.show();
	}
}

public class Client {
	public static void main(final String[] args) {
		System.out.println("big image:");
		final Image bigImage = new BigImage();
		bigImage.show();

		System.out.println("image proxy:");
		final Image imageProxy = new ImageProxy();
		imageProxy.show();
	}
}

3. Copy-on-Write代理: 虚拟代理的一种，把复制（克隆）拖延到只有在客户端需要时，才真正采取行动。

4. 保护代理(Protection or Access Proxy)：控制对原始对象的访问。保护代理用于对象应该有不同的访问权限的时候。

5. 智能指引(Smart Reference)：取代了简单的指针,它在访问对象时执行一些附加操作.