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

1 package proxy;
2 
3 public interface Movable {
4     public void move();
5 }

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

 1 package proxy;
 2 
 3 import java.io.File;
 4 import java.io.FileWriter;
 5 import java.lang.reflect.Constructor;
 6 import java.net.URL;
 7 import java.net.URLClassLoader;
 8 
 9 import javax.tools.JavaCompiler;
10 import javax.tools.JavaCompiler.CompilationTask;
11 import javax.tools.StandardJavaFileManager;
12 import javax.tools.ToolProvider;
13 
14 public class Proxy {
15 
16     public static Object newProxyInstance() throws Exception {
17         String rt = "\n\r";
18         
19         //动态代理文件的源码
20         String str = 
21         "package proxy;" + rt +
22 
23         "public class TankTimeProxy implements Movable {"+rt+
24 
25             "private Movable m;" + rt +
26             
27             "public TankTimeProxy(Movable m) {" + rt +
28                 "this.m = m;" + rt +
29             "}" + rt +
30 
31             "@Override" + rt +
32             "public void move() {" + rt +
33                 "System.out.println(\"Time Proxy start...........\");" + rt +
34                 "long start = System.currentTimeMillis();" + rt +
35                 "m.move();" + rt +
36                 "long end = System.currentTimeMillis();" + rt +
37                 "System.out.println(\"花费时间：\"+(end - start));" + rt +
38                 "System.out.println(\"Time Proxy end...........\");" + rt +
39             "}" + rt +
40 
41         "}" ;
42         
43         //把源码写到java文件里
44         File file = new File(System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.java");
45         FileWriter fw = new FileWriter(file);
46         fw.write(str);
47         fw.flush();
48         fw.close();
49         
50         //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
51         JavaCompiler jc = ToolProvider.getSystemJavaCompiler();
52         
53         //文件管事器
54         StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null);
55         
56         //编译单元
57         Iterable units = fileMgr.getJavaFileObjects(file);
58         
59         //编译任务
60         CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);
61         
62         //编译
63         t.call();    
64         fileMgr.close();
65         
66         //把类load到内存里
67         URL[] urls = new URL[] {new URL("file:/"+System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.class")};
68         URLClassLoader uc = new URLClassLoader(urls);
69         Class c = uc.loadClass("proxy.TankTimeProxy");
70         
71         //生成实例
72         //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
73         Constructor ctr = c.getConstructor(Movable.class);
74         return ctr.newInstance(new Tank());
75     }
76 }

4.Client.java

 1 package proxy;
 2 
 3 import java.io.IOException;
 4 
 5 import org.junit.Test;
 6 
 7 public class Client {
 8 
 9     @Test
10     public void testProxy() throws Exception{
11         
12         Movable m = (Movable)Proxy.newProxyInstance();
13         m.move();
14         
15     }
16 }

三、运行结果