一个ClassLoader的简单例子

在Jsp 容器中，在不同的webapp下，是可以存在相同的类的，那么jsp容器是怎么实现的呢，今天写了个简单的例子，和大家一起分享一下。

首先写一个个App的类：

public class App implements Runnable{public void run(){System.out.println("this is first app!");}} 

app代表一个webapp，把app编译的class文件copy到目录file:///workspace/ClassLoader/app1/目录下。

把App代码修改一下，将first改成second,把编译的class文件copy到目录file:///workspace/ClassLoader/app2/下。

在写一个模拟的容器类Main:

import java.net.MalformedURLException;import java.net.URL;import java.net.URLClassLoader;/** * Class loader的测试 * * @author markzhang * */public class Main {public static void app1() {try {URL[] urls = new URL[1];urls[0] = new URL("file:///workspace/ClassLoader/app1/");URLClassLoader cl = new URLClassLoader(urls, Thread.currentThread().getContextClassLoader());Class c = Class.forName("App", false, cl);System.out.println(c.getClassLoader());Object obj = c.newInstance();Runnable a = (Runnable) obj;a.run();}catch (MalformedURLException e) {e.printStackTrace();}catch (ClassNotFoundException e) {e.printStackTrace();}catch (InstantiationException e) {e.printStackTrace();}catch (IllegalAccessException e) {e.printStackTrace();}}public static void app2() {try {URL[] urls = new URL[1];urls[0] = new URL("file:///workspace/ClassLoader/app2/");URLClassLoader cl = new URLClassLoader(urls, Thread.currentThread().getContextClassLoader());Class c = Class.forName("App", false, cl);System.out.println(c.getClassLoader());Object obj = c.newInstance();Runnable a = (Runnable) obj;a.run();}catch (MalformedURLException e) {e.printStackTrace();}catch (ClassNotFoundException e) {e.printStackTrace();}catch (InstantiationException e) {e.printStackTrace();}catch (IllegalAccessException e) {e.printStackTrace();}}public static void main(String[] args) {app1();app2();}} 

把App源代码删除

 

运行：

 

java.net.URLClassLoader@c17164

this is first app

java.net.URLClassLoader@61de33

this is second app