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。