Action ***cannot be found in the namespace

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>
<package name="action" extends="struts-default">
<action name="lookMessage" class="action.LookMessage">//命名空间namespace
<result name="success">/lookMessage.jsp</result>
<result name="input">/index.jsp</result>
</action>
<action name="addMessage" class="action.AddMessage">
<result name="success" type="chain">lookMessage</result>//与命名空间保持一致而不是类名
<result name="input">/addMessage.jsp</result>
</action>

</package>
</struts>