java -- java.lang.reflect.proxy分析

proxy使用

实例1

http://www.cnblogs.com/linjiqin/archive/2011/02/18/1957600.html

实例2

/*
*Copyright (c) 2016, gp.inc and/or its affiliates. All rights reserved.
*/
package com.proxy.demo2;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

public class ProxyStudy {

    @SuppressWarnings("all")
    public static void main(String[] args) throws Exception {
        ClassLoader loader = Collection.class.getClassLoader();
        Class[] interfaces = new Class[] { Collection.class };

        InvocationHandler h = new InvocationHandler() {
            // proxyBuildColl是对ArrayList进行代理
            ArrayList target = new ArrayList();

            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println(method.getName() + "执行之前...");
                if (null != args) {
                    System.out.println("方法的参数：" + Arrays.asList(args));
                } else {
                    System.out.println("方法的参数：" + null);
                }
                Object result = method.invoke(target, args);
                System.out.println(method.getName() + "执行之后...");
                return result;
            }
        };

        Collection proxyBuildCollection2 = (Collection) Proxy.newProxyInstance(loader, interfaces, h);

        proxyBuildCollection2.add("abc");
        proxyBuildCollection2.size();
        proxyBuildCollection2.clear();
        proxyBuildCollection2.getClass().getName();
    }
}

简述

动态代理，代理一个对象，间接执行相关操作，并且在执行操作前后可以增加额外操作，如日志。

应用场景

spring框架AOP中核心采用动态代理
org.springframework.aop.framework.CglibAopProxy
org.springframework.aop.framework.JdkDynamicAopProxy
两种动态代理的实现。

分析java.lang.reflect.Proxy

静态方法

方法newProxyInstance 是我们经常用到的，返回目标对象。

Collection proxyBuildCollection2 = (Collection) Proxy.newProxyInstance(loader, interfaces, h);

源码

    @CallerSensitive
    public static Object newProxyInstance(ClassLoader loader,
                                          Class[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {
        if (h == null) {
            throw new NullPointerException();
        }

        final Class[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }

        /*
         * Look up or generate the designated proxy class.
         */
        Class cl = getProxyClass0(loader, intfs);

        /*
         * Invoke its constructor with the designated invocation handler.
         */
        try {
            final Constructor cons = cl.getConstructor(constructorParams);
            final InvocationHandler ih = h;
            if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
                // create proxy instance with doPrivilege as the proxy class may
                // implement non-public interfaces that requires a special permission
                return AccessController.doPrivileged(new PrivilegedAction