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

 

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