strut2开发环境搭建时遇到的问题
大家好，我在配置strut2的时候，启动tomcat后发生这样的错误

严重: Exception starting filter struts2
java.lang.ClassNotFoundException: org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:532)
at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:514)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:133)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:256)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:382)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:103)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4650)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5306)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:618)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1100)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1618)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)

三月 20, 2013 9:49:15 下午 org.apache.catalina.core.StandardContext startInternal
严重: Error filterStart


弄了一天了，还是没弄好，请给小弟指点，谢谢！！！！
我的web.xml文件配置如下：

<?xml version="1.0" encoding="UTF-8"?>

<web-app id="WebApp_9" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" 

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">



    



    <filter>

        <filter-name>struts2</filter-name>

        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>

    </filter>



    <filter-mapping>

        <filter-name>struts2</filter-name>

        <url-pattern>/*</url-pattern>

    </filter-mapping>



    <welcome-file-list>

        <welcom