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 = "

";
        
        //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