（tomcat中级）应用Tomcat的WebappClassLoader加载指定目录的jar文件要点用WebappClassLoader::addRepositor
（tomcat中级）应用Tomcat的WebappClassLoader加载指定目录的jar文件
要点
用WebappClassLoader::addRepository就可以实现。不用扩展WebappClassLoader类。当ServletContextListener::contextInitialized时，调用addRepository。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";@Overridepublic void contextInitialized(ServletContextEvent event) {ServletContext context = event.getServletContext();addJar(context);}@Overridepublic 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"?><!DOCTYPE web-app 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.extlibs</param-name> <param-value>/../../extlib,/../../otherlib</param-value> </context-param> <listener> <listener-class>cn.net.tianyu.classloader.servlet.ClassLoadListener</listener-class> </listener><servlet><servlet-name>sample</servlet-name><servlet-class>cn.net.tianyu.classloader.servlet.SampleServlet</servlet-class></servlet><servlet-mapping><servlet-name>sample</servlet-name><url-pattern>/sample</url-pattern></servlet-mapping></web-app>
1 楼 stevendu 2009-09-09 执行到 WebappClassLoader loader = (WebappClassLoader) getClass().getClassLoader(); 时报错！
严重: Exception sending context initialized event to listener instance of class com.zoove.dcp.jars.JarLoaderListener
java.lang.ClassCastException: org.apache.catalina.loader.WebappClassLoader cannot be cast to org.apache.catalina.loader.WebappClassLoader
at com.zoove.dcp.jars.JarLoaderListener.addJar(JarLoaderListener.java:35)
at com.zoove.dcp.jars.JarLoaderListener.contextInitialized(JarLoaderListener.java:25)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3843)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4350)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:791)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:771)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:525)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:924)
at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:887)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:492)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1147)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1053)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
at org.apache.catalina.core.StandardService.start(StandardService.java:516)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
at org.apache.catalina.startup.Catalina.start(Catalina.java:578)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
2009-9-9 23:41:47 org.apache.catalina.core.StandardContext start
严重: Error listenerStart
2009-9-9 23:41:47 org.apache.catalina.core.StandardContext start
严重: Context [/dcp] startup failed due to previous errors
2 楼 stevendu 2009-09-09 难道是我的jar包用错了？ 我用的catalina.jar啊。 3 楼 stevendu 2009-09-10 问题找到了，我应该在部署后的lib中删除catalina.jar 4 楼 mahengyang 2011-09-16 为什么用tomcat启动web工程时需要将用到的jar包都放在WEB-INF/lib目录下呢？我在工程里的BuildPath里也设置了需要的jar包的路径，但是程序运行后还是会报出CLASSNOTFOUNDEXCEPTION，当我把所有的jar包都放到WEB-INF/lib下面后就好了。
