（tomcat中级）应用Tomcat的WebappClassLoader加载指定目录的jar文件

要点

1. 用WebappClassLoader::addRepository就可以实现。不用扩展WebappClassLoader类。
2. 当ServletContextListener::contextInitialized时，调用addRepository。
3. 在各个context-param中指定jar所在路径。

ServletContextListener

 package cn.net.tianyu.classloader.servlet;

 import java.io.File;
 import java.io.FilenameFilter;
 import java.net.MalformedURLException;
 import java.util.StringTokenizer;

 import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletContextListener;

 import org.apache.catalina.loader.WebappClassLoader;

 public class ClassLoadListener implements ServletContextListener {

     private static final String CONTEXT_PARAM_NAME_EXTLIBPATH = "net.tianyu.servlet.extlibs";

     @Override
     public void contextInitialized(ServletContextEvent event) {
         ServletContext context = event.getServletContext();
         addJar(context);
     }

     @Override
     public void contextDestroyed(ServletContextEvent event) {

     }

     synchronized private void addJar(ServletContext context) {

         String extlibs = context.getInitParameter(CONTEXT_PARAM_NAME_EXTLIBPATH);

         if (extlibs == null || extlibs.length() == 0)
             return;

         WebappClassLoader loader = (WebappClassLoader) getClass().getClassLoader();

         StringTokenizer st = new StringTokenizer(extlibs, ",");
         while (st.hasMoreTokens()) {
             String jarPath = st.nextToken();
             String jarRealPath = context.getRealPath(jarPath);

             File jarDir = new File(jarRealPath);
             if (!jarDir.isDirectory())
                 continue;
             File[] jarFiles = jarDir.listFiles(new JarFileNameFilter());
             for (File jarFile : jarFiles) {
                 try {
                     loader.addRepository(jarFile.toURI().toURL().toString());
                 } catch (MalformedURLException e) {
                 }
             }
         }
     }

     class JarFileNameFilter implements FilenameFilter {
         public boolean accept(File dir, String name) {
             return name.toLowerCase().endsWith(".jar");
         }
     }

 }

 web.xml

 xml version="1.0" encoding="Shift_JIS"?>


     PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
     "http://java.sun.com/dtd/web-app_2_3.dtd">

 <web-app>
   <context-param>
     <param-name>net.tianyu.servlet.extlibsparam-name>
     <param-value>/../../extlib,/../../otherlibparam-value>
   context-param>

   <listener>
     <listener-class>cn.net.tianyu.classloader.servlet.ClassLoadListenerlistener-class>
   listener>

     <servlet>
         <servlet-name>sampleservlet-name>
         <servlet-class>cn.net.tianyu.classloader.servlet.SampleServletservlet-class>
     servlet>
     <servlet-mapping>
         <servlet-name>sampleservlet-name>
         <url-pattern>/sampleurl-pattern>
     servlet-mapping>
 web-app>