Proxy

意图：为其他对象提供一种代理以控制对这个对象的访问。

主要解决：在直接访问对象时带来的问题，比如说：要访问的对象在远程的机器上.在面向对象系统中，有些对象由于某些原因（比如对象创建开销很大，或者某些操作需要安全控制，或者需要进程外的访问），直接访问会给使用者或者系统结构带来很多麻烦，我们可以在访问此对象时加上一个对此对象的访问层

什么时候使用：想在访问一个类时做一些控制

如何解决 ：增加中间层

使用场景：按职责来划分，通常有一下使用场景：1.远程代理 2.虚拟代理 3.Copy-on-Write代理 4.保护（Protect or Access）代理 5.Cache代理 6.防火墙（Firewall）代理 7.同步化（Synchronization）代理 7.智能引用（Smart Reference）代理

注意事项：1.和适配器模式的区别：适配器模式主要改变所考虑对象的接口，而代理迷失不能改变所代理类的接口 2.和装饰模式的区别：装饰模式为了增强功能，而代理模式是为了加以控制

1. 模拟Proxy 类
   

   package com.bjsxt.proxy;
   
   public interface Moveable {
   	void move();
   	
   }
   

   
   

   package com.bjsxt.proxy;
   
   import java.util.Random;
   
   
   public class Tank implements Moveable {
   
   	@Override
   	public void move() {
   		
   		System.out.println("Tank Moving...");
   		try {
   			Thread.sleep(new Random().nextInt(10000));
   		} catch (InterruptedException e) {
   			e.printStackTrace();
   		}
   		
   	}
   
   	
   	
   }
   

   
   

   package com.bjsxt.proxy;
   
   import java.io.File;
   import java.io.FileWriter;
   import java.lang.reflect.Constructor;
   import java.lang.reflect.Method;
   import java.net.URL;
   import java.net.URLClassLoader;
   
   import javax.tools.JavaCompiler;
   import javax.tools.StandardJavaFileManager;
   import javax.tools.ToolProvider;
   import javax.tools.JavaCompiler.CompilationTask;
   
   public class Proxy {
   	public static Object newProxyInstance(Class infce, InvocationHandler h) throws Exception { //JDK6 Complier API, CGLib, ASM
   		String methodStr = "";
   		String rt = "\r\n";
   		
   		Method[] methods = infce.getMethods();
   		/*
   		for(Method m : methods) {
   			methodStr += "@Override" + rt + 
   						 "public void " + m.getName() + "() {" + rt +
   						 	"   long start = System.currentTimeMillis();" + rt +
   							"   System.out.println(\"starttime:\" + start);" + rt +
   							"   t." + m.getName() + "();" + rt +
   							"   long end = System.currentTimeMillis();" + rt +
   							"   System.out.println(\"time:\" + (end-start));" + rt +
   						 "}";
   		}
   		*/
   		for(Method m : methods) {
   			methodStr += "@Override" + rt + 
   						 "public void " + m.getName() + "() {" + rt +
   						 "    try {" + rt +
   						 "    Method md = " + infce.getName() + ".class.getMethod(\"" + m.getName() + "\");" + rt +
   						 "    h.invoke(this, md);" + rt +
   						 "    }catch(Exception e) {e.printStackTrace();}" + rt +
   						
   						 "}";
   		}
   		
   		String src = 
   			"package com.bjsxt.proxy;" +  rt +
   			"import java.lang.reflect.Method;" + rt +
   			"public class $Proxy1 implements " + infce.getName() + "{" + rt +
   			"    public $Proxy1(InvocationHandler h) {" + rt +
   			"        this.h = h;" + rt +
   			"    }" + rt +
   			
   			
   			"    com.bjsxt.proxy.InvocationHandler h;" + rt +
   							
   			methodStr +
   			"}";
   		String fileName = 
   			"d:/src/com/bjsxt/proxy/$Proxy1.java";
   		File f = new File(fileName);
   		FileWriter fw = new FileWriter(f);
   		fw.write(src);
   		fw.flush();
   		fw.close();
   		
   		//compile
   		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
   		StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
   		Iterable units = fileMgr.getJavaFileObjects(fileName);
   		CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
   		t.call();
   		fileMgr.close();
   		
   		//load into memory and create an instance
   		URL[] urls = new URL[] {new URL("file:/" + "d:/src/")};
   		URLClassLoader ul = new URLClassLoader(urls);
   		Class c = ul.loadClass("com.bjsxt.proxy.$Proxy1");
   		System.out.println(c);
   		
   		Constructor ctr = c.getConstructor(InvocationHandler.class);
   		Object m = ctr.newInstance(h);
   		//m.move();
   
   		return m;
   	}
   }
   

   
   

   package com.bjsxt.proxy;
   
   import java.lang.reflect.Method;
   
   public interface InvocationHandler {
   	public void invoke(Object o, Method m);
   }
   

   package com.bjsxt.proxy;
   
    import java.lang.reflect.Method;
   
   public class TimeHandler implements InvocationHandler{
   	private Object target;
   	public TimeHandler(Object target) {
   		super();
   		this.target = target;
   	}
   
   	@Override
   	public void invoke(Object o, Method m) {
   		long start = System.currentTimeMillis();
   		System.out.println("starttime:" + start);
   		System.out.println(o.getClass().getName());
   		try {
   			m.invoke(target);
   		} catch (Exception e) {
   			e.printStackTrace();
   		}
   		long end = System.currentTimeMillis();
   		System.out.println("time:" + (end-start));
   	}
   }
    

   
   

   package com.bjsxt.proxy;
   
   
   public class Client {
   	public static void main(String[] args) throws Exception {
   		Tank t = new Tank();
   		InvocationHandler h = new TimeHandler(t);
   		
   		Moveable m = (Moveable)Proxy.newProxyInstance(Moveable.class, h);
   		
   		m.move();
   	}
   }
   //可以对任意的对象、任意的接口方法，实现任意的代理

   
   
2. 用法示例
   

   package com.bjsxt.proxy.test;
   
   public interface UserMgr {
   	void addUser();
   }
   

   
   

   package com.bjsxt.proxy.test;
   
   public class UserMgrImpl implements UserMgr {
   
   	@Override
   	public void addUser() {
   		System.out.println("1: 插入记录到user表");
   		System.out.println("2: 做日志在另外一张表");
   	}
   	
   }
   

   
   

   package com.bjsxt.proxy.test;
   
   import java.lang.reflect.Method;
   
   import com.bjsxt.proxy.InvocationHandler;
   
   public class TransactionHandler implements InvocationHandler {
   	
   	private Object target;
   	
   	public TransactionHandler(Object target) {
   		super();
   		this.target = target;
   	}
   
   	@Override
   	public void invoke(Object o, Method m) {
   		System.out.println("Transaction Start");
   		try {
   			m.invoke(target);
   		} catch (Exception e) {
   			e.printStackTrace();
   		}
   		System.out.println("Transaction Commit");
   	}
   
   }
   

   
   

   package com.bjsxt.proxy.test;
   
   import com.bjsxt.proxy.InvocationHandler;
   import com.bjsxt.proxy.Proxy;
   import com.bjsxt.proxy.TimeHandler;
   
   public class Client {
   	public static void main(String[] args) throws Exception {
   		UserMgr mgr = new UserMgrImpl();
   		InvocationHandler h = new TransactionHandler(mgr);
   		//TimeHandler h2 = new TimeHandler(h);
   		UserMgr u = (UserMgr)Proxy.newProxyInstance(UserMgr.class,h);
   		u.addUser();
   	}
   }