Java-馬士兵設計模式學習筆記-代理模式-動態代理 調用Proxy.newProxyInstance()

一、概述

1.目標：不自己寫代理類，利用Proxy.newProxyInstance()動態生成

2.用到的知識點：

(1)//編譯源碼，生成class,注意編譯環境要換成jdk才有compiler,單純的jre沒有compiler，會空指針錯誤

JavaCompiler jc = ToolProvider.getSystemJavaCompiler();

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

(3)//編譯單元
Iterable units = fileMgr.getJavaFileObjects(file);

(4)//編譯任務
CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);

(5)//編譯
t.call();

(6)//把類load到內存里

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)//生成實例

//return c.newInstance(); //c.newInstance()會調用無參數的Construtor，若類沒有無參的Constructor時會出錯
Constructor ctr = c.getConstructor(Movable.class);
return ctr.newInstance(new Tank());

 

二、代碼

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";
        
        //動態代理文件的源碼
        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(\"花費時間：\"+(end - start));" + rt +
                "System.out.println(\"Time Proxy end...........\");" + rt +
            "}" + rt +

        "}" ;
        
        //把源碼寫到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();
        
        //編譯源碼，生成class,注意編譯環境要換成jdk才有compiler,單純的jre沒有compiler，會空指針錯誤
        JavaCompiler jc = ToolProvider.getSystemJavaCompiler();
        
        //文件管事器
        StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null);
        
        //編譯單元
        Iterable units = fileMgr.getJavaFileObjects(file);
        
        //編譯任務
        CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);
        
        //編譯
        t.call();    
        fileMgr.close();
        
        //把類load到內存里
        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");
        
        //生成實例
        //return c.newInstance(); //c.newInstance()會調用無參數的Construtor，若類沒有無參的Constructor時會出錯
        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、運行結果