（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>