学习：java设计模式—动态代理模式

类定义：

1、被代理接口和实现类：Tank类实现了Moveable接口，能够move()

package com.zec.disignmode;

public interface Moveable {

    public void move();

}

package com.zec.disignmode;

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();

        }

    }

}

2、代理加工接口和实现类：TimeHandler类实现了InvocationHandler接口，能够invoke（Object object，Method m）在object的m方法前后加上自己记录时间的逻辑，并不是代理类，只是提供了对被代理类的加工逻辑；

package com.zec.disignmode;

import java.lang.reflect.Method;

public interface InvocationHandler {

    public void invoke(Object o,Method m);

}

package com.zec.disignmode;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

public class TimeHandler implements InvocationHandler{

    @Override

    public void invoke(Object object, Method m) {

        System.out.println("Time Before "+m.getName());

        try {

            m.invoke(object);

        } catch (Exception e) {

            e.printStackTrace();

        }

        System.out.println("Time After  "+m.getName());

    }

}

3、生成动态代理类的Proxy静态类：代理产生器，根据传进来的参数Class Intface和InvocationHandler h，产生动态代理类；从而使intface中的所有方法都加上了h中invoke方法的自定义逻辑；为了便于代理类的组合和扩展，代理类也会实现Intface接口，最终返回一个代理类对象；

package com.zec.disignmode;

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 newInstance(Class intface,InvocationHandler h) throws Exception {

        /*Generate the source code*/

        String rt = "\r\n";

        String methodStr = "";

        for (Method method:intface.getMethods()) {

            methodStr +=

            "    @Override"+rt+

            "    public void "+ method.getName() +"() {"+rt+

            "        try{"+rt+

            "            Method m = "+ intface.getName()+".class.getMethod(\""+ method.getName() +"\");" + rt+

            "            h.invoke(tank,m);"+rt+

            "        }catch(Exception e){e.printStackTrace();}"+rt+

            "    }"+rt

            ;

        }

        String src =

            "package com.zec.disignmode;"+rt+

            "import java.util.Random;"+rt+

            "import java.lang.reflect.*;"+rt+

            "public class TankTimeProxy implements "+ intface.getName() +"{"+rt+

            "    "+ intface.getName() +" tank;"+rt+

            "    com.zec.disignmode.InvocationHandler h;"+rt+

            "    public TankTimeProxy("+ intface.getName() +" t,com.zec.disignmode.InvocationHandler h) {"+rt+

            "        tank = t;"+rt+

            "        this.h = h;"+rt+

            "    }"+rt+

            methodStr+

            "}";

        /*Generate the java file*/

        String fileName = System.getProperty("user.dir")+"/src/com/zec/disignmode/TankTimeProxy.java";

        File f = new File(fileName);

        FileWriter fw = new FileWriter(f);

        fw.write(src);

        fw.flush();

        fw.close();

        /*Generate the class file*/

        JavaCompiler jc = ToolProvider.getSystemJavaCompiler();

        StandardJavaFileManager jfMgr = jc.getStandardFileManager(null, null, null);

        Iterable units = jfMgr.getJavaFileObjects(fileName);

        CompilationTask ct =  jc.getTask(null, jfMgr, null, null, null, units);

        ct.call();

        jfMgr.close();

        /*Load the class into the memory*/

        URL[] urls = new URL[]{new URL("file:/"+System.getProperty("user.dir")+"/src")};

        URLClassLoader urlLoader = new URLClassLoader(urls);

        Class c = urlLoader.loadClass("com.zec.disignmode.TankTimeProxy");

        /*Generate the object*/

        Constructor constructor = c.getConstructor(Moveable.class,InvocationHandler.class);

        Object moveable = constructor.newInstance(new Tank(),h);

        return moveable;

    }

}

4、测试类

package com.zec.disignmode;

public class Client {

    public static void main(String[] args) {

        Moveable m = new Tank();

        LogHandler h = new LogHandler();

        try {

            Moveable moveable = (Moveable) Proxy.newInstance(Moveable.class, h);

            moveable.move();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

5、学习心得：

（1）为了增强代理类的可扩展性，代理类和被代理类实现的是同一个接口，这样代理类可以作为被代理类再次被代理，可以实现不同功能代理的组合，本例中为Moveable；

（2）InvocationHandler接口定义了对特定对象的方法的代理加工方法，Proxy为代理生成器，newInstance（Class intface,InvocationHandler h）方法表示对intface接口的所有方法进行加工，加工的逻辑由h的invoke方法定义；

（3）代理生成器最后返回一个intface类型的引用，指向已经生成的动态代理类；

（4）对于使用者来说，不必关心动态代理类的名称，只需要指定要代理的接口类型和处理类就可以了。