Java-马士兵设计模式学习笔记-代理模式-动态代理 调用Proxy.newProxyInstance()

一、概述

1.目标：不自己写代理类，利用Proxy.newProxyInstance()动态生成

2.用到的知识点：

(1)//编译源码，生成class,注意编译环境要换成jdk才有compiler,单纯的jre没有compiler，会空指针错误

JavaCompiler jc = ToolProvider.getSystemJavaCompiler();

(2)//文件管事器
StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null);

(3)//编译单元
Iterable units = fileMgr.getJavaFileObjects(file);

(4)//编译任务
CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);

(5)//编译
t.call();

(6)//把类load到内存里

URL[] urls = new URL[] {new URL("file:/"+System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.class")};
URLClassLoader uc = new URLClassLoader(urls);
Class c = uc.loadClass("proxy.TankTimeProxy");

(7)//生成实例

//return c.newInstance(); //c.newInstance()会调用无参数的Construtor，若类没有无参的Constructor时会出错
Constructor ctr = c.getConstructor(Movable.class);
return ctr.newInstance(new Tank());

二、代码

1.Movable.java

2.Tank.java

3.Proxy.java

4.Client.java

1.Movable.java

 package proxy;

 public interface Movable {
     public void move();
 }

2.Tank.java

package proxy;

import java.util.Random;

public class Tank implements Movable {

    @Override
    public void move() {
        System.out.println("Tank moving.......");
        try {
            Thread.sleep(new Random().nextInt(2000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

3.Proxy.java

 package proxy;

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

 import javax.tools.JavaCompiler;
 import javax.tools.JavaCompiler.CompilationTask;
 import javax.tools.StandardJavaFileManager;
 import javax.tools.ToolProvider;

 public class Proxy {

     public static Object newProxyInstance() throws Exception {
         String rt = "\n\r";

         //动态代理文件的源码
         String str =
         "package proxy;" + rt +

         "public class TankTimeProxy implements Movable {"+rt+

             "private Movable m;" + rt +

             "public TankTimeProxy(Movable m) {" + rt +
                 "this.m = m;" + rt +
             "}" + rt +

             "@Override" + rt +
             "public void move() {" + rt +
                 "System.out.println(\"Time Proxy start...........\");" + rt +
                 "long start = System.currentTimeMillis();" + rt +
                 "m.move();" + rt +
                 "long end = System.currentTimeMillis();" + rt +
                 "System.out.println(\"花费时间：\"+(end - start));" + rt +
                 "System.out.println(\"Time Proxy end...........\");" + rt +
             "}" + rt +

         "}" ;

         //把源码写到java文件里
         File file = new File(System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.java");
         FileWriter fw = new FileWriter(file);
         fw.write(str);
         fw.flush();
         fw.close();

         //编译源码，生成class,注意编译环境要换成jdk才有compiler,单纯的jre没有compiler，会空指针错误
         JavaCompiler jc = ToolProvider.getSystemJavaCompiler();

         //文件管事器
         StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null);

         //编译单元
         Iterable units = fileMgr.getJavaFileObjects(file);

         //编译任务
         CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);

         //编译
         t.call();
         fileMgr.close();

         //把类load到内存里
         URL[] urls = new URL[] {new URL("file:/"+System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.class")};
         URLClassLoader uc = new URLClassLoader(urls);
         Class c = uc.loadClass("proxy.TankTimeProxy");

         //生成实例
         //return c.newInstance(); //c.newInstance()会调用无参数的Construtor，若类没有无参的Constructor时会出错
         Constructor ctr = c.getConstructor(Movable.class);
         return ctr.newInstance(new Tank());
     }
 }

4.Client.java

 package proxy;

 import java.io.IOException;

 import org.junit.Test;

 public class Client {

     @Test
     public void testProxy() throws Exception{

         Movable m = (Movable)Proxy.newProxyInstance();
         m.move();

     }
 }

三、运行结果