Struts2中Action中动态调用，为什么出错了？？？

Struts.xml:

<constant name="struts.devMode" value="true" />

     <package name="stu" extends="struts-default" namespace="">

    

      <action name="stu" class="com.stu.strust2.action.IndexAction">

            <result>/hello.jsp</result>

        </action>

    </package>

IndexAction.java:

public class IndexAction extends ActionSupport{

   public String add(){

 return "success";

}

}

index.jsp:

 <a href="<%=path%>/stu/stu!add">Action的案例！</a>

错误：Could not find action or result

There is no Action mapped for action name stu!add. - [unknown location]