为啥使用感叹号的时候报错提示无效的方法，麻烦各位大大帮忙瞧瞧

Action代码

public class HelloWorldAction extends ActionSupport {

/**

* 

*/

private static final long serialVersionUID = 1L;

@Override

public String execute() throws Exception {

System.out.println("执行Action");

return SUCCESS;

}

//添加

public String add(){

System.out.println("执行ADD");

return "add";

}

//更新

public String update(){

System.out.println("执行UPDATE");

return "update";

}

}

struts配置的代码

<struts>

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

<action name="helloWorld" class="com.hao.action.HelloWorldAction">

<result>/result.jsp</result>

<result name="add">/add.jsp</result>

<result name="update">/update.jsp</result>

</action>

</package>

<constant name="struts.enable.DynamicMethodInvocation" value="true"></constant>

</struts>

运行后访问 http://127.0.0.1:8080/HelloWorld/helloWorld!add

报错提示无效的方法