Exception starting filter struts2 java.lang.NullPointerException 解决办法!

org.apache.catalina.core.StandardContext filterStart    
严重: Exception starting filter struts2    
java.lang.NullPointerException    
     at com.opensymphony.xwork2.util.FileManager$FileRevision.needsReloading(FileManager.java:209)    
     at com.opensymphony.xwork2.util.FileManager.fileNeedsReloading(FileManager.java:60)    
     at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.needsReload(XmlConfigurationProvider.java:325)    
     at org.apache.struts2.config.StrutsXmlConfigurationProvider.needsReload(StrutsXmlConfigurationProvider.java:168)    
     at com.opensymphony.xwork2.config.ConfigurationManager.conditionalReload(ConfigurationManager.java:220)    
     at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:61)    
     at org.apache.struts2.dispatcher.Dispatcher.getContainer(Dispatcher.java:774)    
     at org.apache.struts2.dispatcher.FilterDispatcher.init(FilterDispatcher.java:191)    
     at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:275)    
     at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:397)    
     at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:108)    
     at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:3709)    
     at org.apache.catalina.core.StandardContext.start(StandardContext.java:4363)    
     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:926)    
     at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:889)    
     at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:492)    
     at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1149)    
     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(NativeMethodAccessorImpl.java:39)    
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)    
     at java.lang.reflect.Method.invoke(Method.java:597)    
     at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)    
     at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)    
2009-2-4 22:40:54 org.apache.catalina.core.StandardContext start    
严重: Error filterStart    
2009-2-4 22:40:54 org.apache.catalina.core.StandardContext start    
严重: Context [/Struts2Demo2] startup failed due to previous errors