Java-马士兵设计模式学习笔记-代理模式-动态代理 修改成可以任意修改代理逻辑

一、概述

1.目标：动态代理的代理逻辑可以任意修改

2.思路：

(1)要把代理逻辑抽离，站在jvm的角度思考，应独立出InvocationHandler接口，并接收被代理的对象及方法作为参数invoke(Object o, Method m)，并本身作为参数传给newProxyInstance(Class interfze,InvocationHandler handler) 

(2)InvocationHandler本身聚合被代理类target，以便在target的方法前后增加代理逻辑

3.知识点：

(1)按名字找方法java.lang.reflect.Method md = proxy.Movable.class.getMethod("stop");

(2)按"."拆分字符串：String [] parts = m.toString().replace("abstract ", "").split("\.");

二、代码

1.InvocationHandler.java

2.TimeHandler.java

3.Movable.java

4.Tank.java

5.Proxy.java

6.Client.java

1.InvocationHandler.java

package proxy;

import java.lang.reflect.Method;

public interface InvocationHandler {
    public void invoke(Object o, Method m);
}

2.TimeHandler.java

package proxy;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class TimeHandler implements InvocationHandler {

    //保留被代理的对象
    private Object target;
    
    public TimeHandler(Object target) {
        this.target = target;
    }

    @Override
    public void invoke(Object o, Method m) {
        System.out.println("Time Proxy start...........");
        long start = System.currentTimeMillis();
        try {
            //除了静态方法，方法的调用都要先已知对象，所以要把对象o作为参数传进去
            m.invoke(target);    
        } catch (Exception e) {
            e.printStackTrace();
        } 
        long end = System.currentTimeMillis();
        System.out.println("花费时间："+(end - start));
        System.out.println("Time Proxy end...........");

    }

}

3.Movable.java

package proxy;

public interface Movable {
    public void move();
    public void stop();
}

4.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();
        }
    }

    @Override
    public void stop() {
        System.out.println("Tank stopping.......");
        
    }

}

5.Proxy.java

package proxy;

import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
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(Class interfze,InvocationHandler handler) throws Exception {
        
        String rt = "

";
        
        //拼接"实现接口方法"的字符串
        String methodStr = "";
        for(Method m: interfze.getMethods() ){
            
            //取出方法的修饰符和返回值类型
            String [] parts = m.toString().replace("abstract ", "").split("\.");
            String [] parts2 = parts[0].split(" ");
            
            methodStr +=
            "@Override" + rt +
            parts2[0]+" "+parts2[1]+" "+m.getName()+"() {" + rt +
            "try{"+ rt +
                "java.lang.reflect.Method md = " + interfze.getName() + ".class.getMethod(""+m.getName()+"");" + rt +
                //传this进去其实没什么用，invoke实际是调用target的方法m.invoke(target)
                "handler.invoke(this, md);" + rt +
            "}catch(Exception e){"+ rt +
            "    e.printStackTrace();" + rt +
            "}" + rt +
            
                
            "}"+ rt ;
        }
        
        
        //动态代理文件的源码
        String str = 
        "package proxy;" + rt +

        "public class TankTimeProxy implements " + interfze.getName() + " {"+rt+

            
            //聚合Handler
            "private InvocationHandler handler;" + rt +
            
            "public TankTimeProxy(InvocationHandler handler) {" + rt +
                "this.handler = handler;" + rt +
            "}" + rt +

            methodStr + 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(interfze);
        Constructor ctr = c.getConstructor(InvocationHandler.class);
        return ctr.newInstance(handler);
    }
}

6.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(Movable.class, new TimeHandler(new Tank()));
        m.move();
        m.stop();
        
    }
}

三、运行结果