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 = "\n\r";

         //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