（2）DiapacthAction

    DispatchAction用于分发的Action,主要的好处是把一些功能类似的Action放到一个Action中，通过传入的不同参数来觉得执行哪个操作.

1. 创建一个类继承DispacthAction,该类中包含多个除方法名称以外其他都和execute()方法一样的多个方法

          public class OperateAction extends DispatchAction {
               public ActionForward add(ActionMapping mapping, ActionForm form,
               HttpServletRequest request, HttpServletResponse response)
               throws Exception {
               System.out.println("Action.add()");
               Cal c = new Cal();
               CalForm f =(CalForm)form;
               double r = 0.0;
               ActionMessages errors = new ActionMessages();
               try{
                     r = c.add(Double.parseDouble(f.getFirst()),Double.parseDouble(f.getSecond()));
               }catch(Exception e){
                     errors.add("num",new ActionMessage("error"));
                     this.saveErrors(request, errors);
                     return mapping.findForward("input");
              }
              f.setResult(r);
              return mapping.findForward("result");
        }
 public ActionForward sub(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
   throws Exception {
  System.out.println("Action.sub()");
  return mapping.findForward("result");
 }
 public ActionForward mul(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
   throws Exception {
  System.out.println("Action.mul()");
  return mapping.findForward("result");
 }
 public ActionForward div(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
   throws Exception {
  System.out.println("Action.div()");
  return mapping.findForward("result");
 }
}

2. 在struts-config.xml文件中进行配置，为该Action配置parameter属性

   <action-mappings >
    <action
      name="CalForm"
      scope="request"
      path="/add"
      type="com.rhcj.struts.CalAction">
      <forward name="result" path="/result.jsp" />
    </action>
    <action path="/operate"
      type="com.rhcj.struts.OperateAction"
      name="CalForm"
      scope="request"
      parameter="operate">
      <forward name="result" path="/result.jsp" />
      <forward name="input" path="/index.jsp"></forward>
    </action>
   </action-mappings>

3.    创建页面，页面请求中要有一个参数与parameter属性值一致，如：/operate?operate=add，此处表单中使用隐藏域传值

   <input type="hidden" name="operate" value="">
    <input type="button" value="+" name="button1"
     onclick="doSubmit('add')">
    <input type="button" value="-" name="button1"
     onclick="doSubmit('sub')">
    <input type="button" value="*" name="button1"
     onclick=doSubmit('mul');>
    <input type="button" value="/" name="button1"
     onclick="doSubmit('div')">
    <script type="text/javascript">
     function doSubmit(oper){
      document.forms[0].elements["operate"].value=oper;
       document.forms[0].submit();
     }
    </script>

  

  

注意：该页面中隐藏域的name属性<input type="hidden" name="operate">对应于struts-config.xml中DispacthAction配置的parameter属性值

<action path="/operate"

        type="com.rhcj.struts.OperateAction"

        name="CalForm"

        scope="request"

        parameter="operate">

      <forward name="result" path="/result.jsp" />

</action>

隐藏域的value值要和DispacthAction中的方法名称对应