【java设计模式】代理模式

计算类中方法运行时间的几种方案：

Client:

 package com.tn.proxy;

 public class Client {
     public static void main(String[] args) {
         /* Car car=new Car();
         car.move(); */

         //通过继承计算方法的运行时间
         /* CarTimeByExtends ctp=new CarTimeByExtends();
         ctp.move(); */

         //通过聚合计算类中方法运行时间
         /* Car car=new Car();
         CarTimeByAggregate ctba=new CarTimeByAggregate(car);
         ctba.getCarRunningTime(); */
     }
 }

Movable:

 package com.tn.proxy;

 public interface Movable {
     void move();
     void stop();
 }

Car:

 package com.tn.proxy;

 import java.util.Random;

 public class Car implements Movable {

     @Override
     public void move() {
         /**
          * 方法内的两段注释代码为给move()方法增加日志及计算方法执行时间。
          */
         /* long start=System.currentTimeMillis();
         System.out.println("Car is start moving..."+start); */
         System.out.println("Car is moving...");
         try {
             Thread.sleep(new Random().nextInt(1500));
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
         /* long end=System.currentTimeMillis();
         System.out.println("Car is stop moving..."+end);
         System.out.println("Car running time is "+(end-start)); */
     }

     @Override
     public void stop() {
         System.out.println("Car is stopped.");
     }

 }

CarTimeByExtends:

 package com.tn.proxy;
 /**
  * 通过继承计算类中方法的运行时间
  * @author xiongjiawei
  *
  */
 public class CarTimeByExtends extends Car{
     @Override
     public void move() {
         long start=System.currentTimeMillis();
         super.move();
         long end=System.currentTimeMillis();
         System.out.println("Car running time is:"+(end-start));
     }
 }

CarTimeByAggregate:

 package com.tn.proxy;
 /**
  * 通过聚合计算方法运行时间
  * @author xiongjiawei
  *
  */
 public class CarTimeByAggregate {
     Car car;

     public CarTimeByAggregate(Car car){
         this.car=car;
     }

     public void getCarRunningTime(){
         long start=System.currentTimeMillis();
         car.move();
         long end=System.currentTimeMillis();
         System.out.println("Car running time is:"+(end-start));
     }
 }

---

通过静态代理实现以上功能：

Client:

 package com.tn.proxy;

 public class Client {
     public static void main(String[] args) {
         Car car=new Car();
         CarTimeProxy ctp=new CarTimeProxy(car);
         CarLogProxy clp=new CarLogProxy(ctp);
         clp.move();
         /*    运行结果：Car被时间包装，时间被日志包装
              logging...
             start time:1494730233358
             Car is moving...
             end time:1494730234835
             logged.
          */
         System.out.println("--------------------------------------");
         Movable clp2=new CarLogProxy(car);
         Movable ctp2=new CarTimeProxy(clp2);
         ctp2.move();
         /*
         运行结果：时间包装日志，日志包装car
         start time:1494730473747
         logging...
         Car is moving...
         logged.
         end time:1494730474995
         */
     }
 }

Movable:

 package com.tn.proxy;

 public interface Movable {
     void move();
 }

Car:

 package com.tn.proxy;

 import java.util.Random;

 public class Car implements Movable {

     @Override
     public void move() {
         System.out.println("Car is moving...");
         try {
             Thread.sleep(new Random().nextInt(1500));
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
     }
 }

CarTimeProxy:

 package com.tn.proxy;

 public class CarTimeProxy implements Movable{
     Movable movable;
     public CarTimeProxy(Movable movable){
         this.movable=movable;
     }
     @Override
     public void move() {
         long start=System.currentTimeMillis();
         System.out.println("start time:"+start);
         movable.move();
         long end=System.currentTimeMillis();
         System.out.println("end time:"+end);
     }
 }

CarLogProxy:

 package com.tn.proxy;

 public class CarLogProxy implements Movable {
     Movable movable;

     public CarLogProxy(Movable movable){
         this.movable=movable;
     }

     @Override
     public void move() {
         System.out.println("logging...");
         movable.move();
         System.out.println("logged.");
     }

 }

---

利用反射动态加载：

 package com.tn.proxy2;

 import java.io.File;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.net.URL;
 import java.net.URLClassLoader;

 import javax.tools.JavaCompiler;
 import javax.tools.JavaCompiler.CompilationTask;

 import com.tn.proxy.Car;
 import com.tn.proxy.Movable;

 import javax.tools.StandardJavaFileManager;
 import javax.tools.ToolProvider;

 public class Test {
     public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
         String rt="\r\t";
         String str=
                 "package com.tn.proxy;"+rt+

         "public class CarTimeProxy implements Movable{"+rt+
         "    Movable movable;"+rt+
         "    public CarTimeProxy(Movable movable){"+rt+
         "        this.movable=movable;"+rt+
         "    }"+rt+
         "    @Override"+rt+
         "    public void move() {"+rt+
         "        long start=System.currentTimeMillis();"+rt+
         "        System.out.println(\"start time:\"+start);"+rt+
         "        movable.move();"+rt+
         "        long end=System.currentTimeMillis();"+rt+
         "        System.out.println(\"end time:\"+end);"+rt+
         "    }"+rt+
         "}";

         //源代码文件生成
         String fileName=System.getProperty("user.dir")
                         +"/src/com/tn/proxy/CarTimeProxy.java";
 //        System.out.println(fileName);
         File f=new File(fileName);
         FileWriter fw=new FileWriter(f);
         fw.write(str);
         fw.flush();
         fw.close();

         //编译
         JavaCompiler compiler=ToolProvider.getSystemJavaCompiler();
 //        System.out.println(compiler.getClass().getName());
         StandardJavaFileManager fMgr=compiler.getStandardFileManager(null, null, null);
         Iterable iterable=fMgr.getJavaFileObjects(fileName);
         CompilationTask ct=compiler.getTask(null, fMgr, null, null, null, iterable);
         ct.call();
         fMgr.close();

         //载入内存，创建类对象实例
         URL[] urls=new URL[]{new URL("file:/"+System.getProperty("user.dir")+"/src")};
         URLClassLoader ul=new URLClassLoader(urls);
         Class c=ul.loadClass("com.tn.proxy.CarTimeProxy");
         ul.close();
 //        System.out.println(c);

         Constructor constructor=c.getConstructor(Movable.class);
         Movable movable=(Movable)constructor.newInstance(new Car());
         movable.move();
     }
 }