Exception starting filter struts2 Line: 209 -com/opensymphony/xwork2/spring/SpringObjectFactory.java:209:-1

启动服务器时出现异常：

警告: Failed startup of context com.google.apphosting.utils.jetty.DevAppEngineWebAppContext@1242b11{/,E:/workspace/uploadPhoto/war}

Class: com.opensymphony.xwork2.spring.SpringObjectFactory
File: SpringObjectFactory.java
Method: getClassInstance
Line: 209 - com/opensymphony/xwork2/spring/SpringObjectFactory.java:209:-1
Caused by: java.lang.NullPointerException  at com.opensymphony.xwork2.spring.SpringObjectFactory.getClassInstance(SpringObjectFactory.java:209)

因为配置了

<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>

</filter>

去掉就没错了 但是不知道为什么。。。 看到的希望大家帮忙解释一下。。