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]