（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"?>

<!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>

评论

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。

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

2 楼 stevendu 2009-09-09  

难道是我的jar包用错了？ 我用的catalina.jar啊。

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