package com.itcast.day3;import java.io.ObjectInputStream.GetField;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.Collection;/** * 通过反射打印出 代理类的 构造函数、方法以及其参数列表 * @author liujl * */public class ProxyTest { public static void main(String[] args) throws Exception{ Class clazzProxy=Proxy.getProxyClass(Collection.class.getClassLoader(), Collection.class); System.out.println(clazzProxy); System.out.println("---------------begin constructors list-----------------"); Constructor[] constructors=clazzProxy.getConstructors(); for(Constructor constructor:constructors){ String name=constructor.getName(); StringBuilder sb=new StringBuilder(name); sb.append("("); Class[] clazzParams=constructor.getParameterTypes(); for(Class clazzParam:clazzParams){ sb.append(clazzParam.getName()); } if(clazzParams!=null&&clazzParams.length!=0) sb.deleteCharAt(sb.length()-1); sb.append(")"); System.out.println(sb); } System.out.println("---------------begin methods list-----------------"); Method[] methods=clazzProxy.getMethods(); for(Method method:methods){ String name=method.getName(); StringBuilder sb=new StringBuilder(name); sb.append("("); Class[] clazzParams=method.getParameterTypes(); for(Class clazzParam:clazzParams){ sb.append(clazzParam.getName()).append(","); } if(clazzParams!=null&&clazzParams.length!=0) sb.deleteCharAt(sb.length()-1); sb.append(")"); System.out.println(sb); } System.out.println("---------------begin create instance object----------------");// clazzProxy.newInstance();//这样不行,这样只会掉那个不带参数的构造方法,而代理对象没有无参构造 //第一种方式创建实例 Constructor constructor=clazzProxy.getConstructor(InvocationHandler.class); class MyInvocationHander1 implements InvocationHandler{ @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return null; } } Collection proxy1=(Collection) constructor.newInstance(new MyInvocationHander1()); System.out.println(proxy1.toString()); proxy1.clear();// proxy1.size();//java.lang.NullPointerException //第二种方式创建实例 Collection proxy2=(Collection)constructor.newInstance(new InvocationHandler(){ @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return null; } }); //第三种方式创建代理类的实例, 得到Class 和 创建实例对象 一步到位 Collection proxy3=(Collection)Proxy.newProxyInstance(Collection.class.getClassLoader(), new Class[]{Collection.class}, new InvocationHandler() { ArrayList target=new ArrayList();//类变量 @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { StringBuilder sbMethodAndParams=new StringBuilder(); sbMethodAndParams.append(method.getName()).append("("); if(args!=null){ for(Object obj : args){ sbMethodAndParams.append(obj.toString()).append(","); } if(args!=null&&args.length!=0){ sbMethodAndParams.deleteCharAt(sbMethodAndParams.length()-1); } } sbMethodAndParams.append(")"); System.out.println(sbMethodAndParams); long beginTime=System.currentTimeMillis(); Object retVal=method.invoke(target, args); long endTime=System.currentTimeMillis(); System.out.println(method.getName()+"执行时间 "+(endTime-beginTime)+" 毫秒"); return retVal; } }); proxy3.clear(); proxy3.add("ljl"); proxy3.add("wiseq"); proxy3.add("traits"); System.out.println("集合元素的个数="+proxy3.size()); //Proxy也是肯定继承自Object , //proxy3.getClass()为啥不调用目标类的getClass()得到ArrayList的字节码? //那是因为Object只有三个方法委托给了InvocationHander, 分别是 toString 、hashCode 、 equals ,而getClass()方法,生成的代理类有自己的实现 System.out.println(proxy3.getClass().getName()); }}
原标题:jdk动态代理
关键词:jdk