严重: Exception starting filter struts2

异常情况如下:

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:221)
	at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:302)
	at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:78)
	at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:3635)
	at org.apache.catalina.core.StandardContext.start(StandardContext.java:4222)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:760)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:740)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:544)
	at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:927)
	at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:890)
	at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:492)
	at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1150)
	at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
	at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:120)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1022)
	at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
	at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
	at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
	at org.apache.catalina.core.StandardService.start(StandardService.java:448)
	at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
	at org.apache.catalina.startup.Catalina.start(Catalina.java:552)
	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:585)
	at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:295)
	at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:433)
2009-3-11 14:26:55 org.apache.catalina.core.StandardContext start
严重: Error filterStart
2009-3-11 14:26:55 org.apache.catalina.core.StandardContext start
严重: Context [/Strust2Demo] startup failed due to previous errors

查看XML。如下

查看下，
web.xml如下

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 <filter>
  <display-name>struts2 for demo</display-name>
  <filter-name>struts2</filter-name>
  <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
 [color=darkred] <init-param>
    <param-name>struts.custom.i18n.resources</param-name>
    <param-value>com.demo.struts.actions.messageResources</param-value>
  </init-param>
  <init-param>
   <param-name>struts.devMode</param-name>
   <param-value>true</param-value>
  </init-param>
  <init-param>
   <param-name>struts.serve.static.browserCache</param-name>
   <param-value>false</param-value>
  </init-param>
  <init-param>
   <param-name>struts.i18n.reload</param-name>
   <param-value>true</param-value>
  </init-param>
  <init-param>
   <param-name>struts.configuration.xml.reload</param-name>
   <param-value>true</param-value>
  </init-param>
  [/color]
 </filter>
 <filter-mapping>
  <filter-name>struts2</filter-name>
  <url-pattern>/*</url-pattern>
 </filter-mapping>
 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
  <welcome-file>index.html</welcome-file>
 </welcome-file-list>

</web-app>

上面标记的部分是在添加之后，出现的异常。
从网上查看资料之后，把这部分去掉，只留下
<init-param>
<param-name>struts.custom.i18n.resources</param-name>
<param-value>com.demo.struts.actions.messageResources</param-value>
</init-param>
一切正常。
具体原因，还没有弄清楚。估计是从struts-default继承下来的，没有自己扩展 Configurationprovider类。
期待高人指点。