配置Structs2所有界面都404

 错误界面
HTTP Status 404 - --------------------------------------------------------------------------------type Status reportmessage description The requested resource () is not available.
--------------------------------------------------------------------------------Apache Tomcat/6.0.32XML配置
  <?xml version="1.0" encoding="UTF-8" ?> 
  <!DOCTYPE struts (View Source for full doctype...)> 
- <struts>
- <!-- 
 
    <constant name="struts.enable.DynamicMethodInvocation" value="false" />
    <constant name="struts.devMode" value="false" />    <include file="example.xml"/>    <package name="default" namespace="/" extends="struts-default">
        <default-action-ref name="index" />
        <action name="index">
            <result type="redirectAction">
                <param name="actionName">HelloWorld</param>
                <param name="namespace">/example</param>
            </result>
        </action>
    </package>
   --> 
  <constant name="struts.devMode" value="true" /> 
- <package name="default" namespace="/" extends="struts-default">
- <action name="hello" class="Action.a.java">
  <result>/Hello.jsp</result> 
  </action>
  </package>
- <!--  Add packages here 
  --> 
  </struts>
WEB配置
<?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">
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  
  <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
    </filter>    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*.action</url-pattern>
    </filter-mapping>
</web-app> 为什么变成那样了 求解释