<struts>  
    <constant name="struts.action.extension" value="do" /> //注意这里
    <package name="default" extends="struts-default"  namespace="/example">
    <action name="HelloWord" class="example.HelloWord">
    <result name="SUCCESS">/example/HelloWord.jsp</result>    
    </action>
    </package>
   <!--  
    <include file="example.xml"/>    
    -->
    <!-- Add packages here -->
</struts>

<init-param>
<param-name>struts.action.extension</param-name>
<param-value>do</param-value>
</init-param>