Java 动态代理学习(一)

Proxy
└── scr
    └── main
        └── java
            ├── main
            │   └── Main.java
            └── proxy
                ├── Moveable.java
                ├── Proxy.java
                └── Tank.java

应用JDK版本 1.7

Main.java

package main;

import proxy.Proxy;

/**
 * 初级 动态代理实现思路
 *
 * @author mao_siyu
 */
public class Main {

    public static void main(String[] args) throws Exception {

        Proxy.newProxyInstance();
    }
}

Moveable.java 接口

package proxy;

public interface Moveable {

    void move();
}

Proxy.java 动态创建代理类

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

/**
 * 马士兵 自定义 动态代理
 * 初级 动态代理实现思路
 *
 * @author mao_siyu
 */
public class Proxy {

    /**
     * java 动态创建类 基于 jdk_1.6 新特性 JavaCompiler
     *
     * @throws Exception
     */
    public static void newProxyInstance() throws Exception {

        String rt = "\r\n";

        StringBuffer sbuffer = new StringBuffer();

        sbuffer.append("       package proxy;                                                                             ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("       import java.util.Random;                                                                   ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("       public class Tank2 implements Moveable {                                                   ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("           public Tank2(Moveable moveable) {                                                      ").append(rt);
        sbuffer.append("               super();                                                                           ").append(rt);
        sbuffer.append("           }                                                                                      ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("           @Override                                                                              ").append(rt);
        sbuffer.append("           public void move() {                                                                   ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("               long start = System.currentTimeMillis();                                           ").append(rt);
        sbuffer.append("               System.out.println(\"tank2 move........\");                                        ").append(rt);
        sbuffer.append("               try {                                                                              ").append(rt);
        sbuffer.append("                   Thread.sleep(new Random().nextInt(10000));                                     ").append(rt);
        sbuffer.append("               } catch (InterruptedException e) {                                                 ").append(rt);
        sbuffer.append("                   e.printStackTrace();                                                           ").append(rt);
        sbuffer.append("               }                                                                                  ").append(rt);
        sbuffer.append("               System.out.println(\"移动时间tank2：\" + (start - System.currentTimeMillis()));    ").append(rt);
        sbuffer.append("           }                                                                                      ").append(rt);
        sbuffer.append("                                                                                                  ").append(rt);
        sbuffer.append("       }                                                                                          ").append(rt);

        String fileName = System.getProperty("user.dir") + "/scr/main/java/proxy/Tank2.java";

        File f = new File(fileName);

        FileWriter fw = new FileWriter(f);
        fw.write(sbuffer.toString());
        fw.flush();
        fw.close();

        /************************************************* 编译文件 *************************************************************/

        // 拿到系统默认的编译器（javac）
        JavaCompiler systemJavaCompiler = ToolProvider.getSystemJavaCompiler();
        // 文件管理器(管理动态生成的文件)
        StandardJavaFileManager fileManager = systemJavaCompiler.getStandardFileManager(null, null, null);
        Iterable compilationUnits = fileManager.getJavaFileObjects(fileName);
        // 编译任务，一次可以编译很多任务
        CompilationTask task = systemJavaCompiler.getTask(null, fileManager, null, null, null, compilationUnits);
        task.call();
        fileManager.close();

        /************************************************* 将文件加载到内存 *************************************************************/
        /**
         * 注意 用classLoader 往内存中load文件的时候， 必须保证这个class 是在classpath里面
         * 所以 这里使用一个特殊的 classLoader
         */
        URL[] urls = new URL[] { new URL("file:/" + System.getProperty("user.dir") + "/scr") };
        @SuppressWarnings("resource")
        URLClassLoader urlLoader = new URLClassLoader(urls);
        Class loadClass = urlLoader.loadClass("proxy.Tank2");
        System.out.println(loadClass);

        /************************************************* 初始化Class *************************************************************/
        // 因为这个类中没有 无参构造方法，所以不能直接使用 newInstance() 初始化;
        Constructor constructor = loadClass.getConstructor(Moveable.class);
        Moveable obj = (Moveable) constructor.newInstance(new Tank());
        obj.move();
    }
}

Tank.java

package proxy;

import java.util.Random;

public class Tank implements Moveable {

    @Override
    public void move() {

        long start = System.currentTimeMillis();
        System.out.println("tank move........");
        try {
            Thread.sleep(new Random().nextInt(10000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("移动时间：" + (start - System.currentTimeMillis()));
    }

}