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 {@Overridepublic 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, ASMString 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();//compileJavaCompiler 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 instanceURL[] 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;}@Overridepublic 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 {@Overridepublic 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;}@Overridepublic 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();}}