运行struts的时候出错，求解答

012-3-7 20:35:56 org.apache.catalina.startup.HostConfig deployDirectory
信息: Deploying web application directory D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\MyStruts
2012-3-7 20:35:57 org.apache.catalina.startup.TaglibUriRule body
信息: TLD skipped. URI: /struts-tags is already defined
2012-3-7 20:35:57 org.apache.catalina.core.StandardContext filterStart
严重: Exception starting filter struts-prepare
java.lang.NoClassDefFoundError: com/opensymphony/xwork2/ActionContext
at org.apache.struts2.dispatcher.ng.InitOperations.cleanup(InitOperations.java:109)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareFilter.init(StrutsPrepareFilter.java:57)
at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:277)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:258)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:382)
at org.apache.catalina.core.ApplicationFilterConfig.(ApplicationFilterConfig.java:103)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4638)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5294)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:895)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:871)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:615)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1095)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1617)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassNotFoundException: com.opensymphony.xwork2.ActionContext
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
... 20 more
2012-3-7 20:35:57 org.apache.catalina.core.StandardContext filterStart
严重: Exception starting filter sitemesh
java.lang.ClassNotFoundException: com.opensymphony.sitemesh.webapp.SiteMeshFilter
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1701)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1546)
at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:525)
at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:507)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:124)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:256)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:382)
at org.apache.catalina.core.ApplicationFilterConfig.(ApplicationFilterConfig.java:103)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4638)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5294)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:895)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:871)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:615)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1095)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1617)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
2012-3-7 20:35:57 org.apache.catalina.core.StandardContext startInternal
严重: Error filterStart
2012-3-7 20:35:57 org.apache.catalina.core.StandardContext startInternal
严重: Context [/MyStruts] startup failed due to previous errors




struts2-core-2.3.1.2.jar  这个jar已经加了，为什么报这样的错呀，求解