DispatchAction 学习

DispatchAction 的作用

DispatchAction的作用简单地说就是把原来我们写在多个acton里的操作放在同一个 action里处理。

在Struts-config 中 相关的配置内容

    <action-mappings>
                <action path= "/welcome" forward= "/index.jsp"/>

                <!-- ======================================= DispatchAction Example -->
                <action path= "/dispatch"    forward= "/dispatch.jsp"/>
                <action path= "/dispatch-submit"    
                                type= "org.apache.struts.webapp.dispatch.DispatchExampleAction"
                                parameter= "dispatchMethod"
                                name= "testForm"
                                scope= "request">
                        <exception key= "dispatch.NoSuchMethodException"
                                             type= "java.lang.NoSuchMethodException"
                                             path= "/dispatch.jsp"/>
                        <exception key= "dispatch.ServletException"
                                             type= "javax.servlet.ServletException"
                                             path= "/dispatch.jsp"/>
                        <forward name= "success" path= "/dispatch.jsp"/>
                </action>
.........

formBean 不在讨论范围，所以省略了。

注意： 【 parameter="dispatchMethod"】。 在后面的JSP 页面中，表单提交的时候，要对dispatchMethod 这个参数赋值。

 

2.提交表单页面

.......
<html:form action= "dispatch-submit" style= "display:inline">
                            <input type= "hidden" name= "dispatchMethod" value= "doFoo" />
                            <html:submit><bean:message key= "button.foo.label" /></html:submit>
                    </html:form>
                             
                    <html:form action= "dispatch-submit" style= "display:inline">
                            <input type= "hidden" name= "dispatchMethod" value= "doBar" />
                            <html:submit><bean:message key= "button.bar.label" /></html:submit>
                    </html:form>
                             
                    <html:form action= "dispatch-submit" style= "display:inline">
                            <input type= "hidden" name= "dispatchMethod" value= "doInvalid" />
                            <html:submit><bean:message key= "method.invalid.label" /></html:submit>
                    </html:form>
                             
                    <html:form action= "dispatch-submit" style= "display:inline">
                            <input type= "hidden" name= "dispatchMethod" value= "execute" />
                            <html:submit><bean:message key= "method.execute.label" /></html:submit>
                    </html:form>
........

 

在这页面中，有专门的一个隐藏域名称为【dispatcherMethod】,和struts-config.xml文件中目标Action 参数[ parameter=dispatcherMethod]相对应。这样Actiton,会根据传入的隐藏域【name=dispatherMethod】的value值，执行相应的方法。

 

1.当提供的dispatcherMethod 的值，在Action中没有对应的方法时（比如，doInvalid),会报

NoSuchMethodException: Action[/dispatch-submit] does not contain specified method (check logs)。

2.如果dispatcherMethod的值为 execute/perform时，报 Do not use 'execute' or 'perform' with DispatchAction.

 

3.如果提供的不提供dispatcherMethod参数时，报错：

ServletException: DispatchMapping[/dispatch-noparam] does not define a handler property

3.在一些demo中，其中有有execute（）,方法，感觉是必须的。但是我把该方法去掉，并没有影响操作。

下面是我删除的代码：

         private ActionDispatcher dispatcher
                                        = new ActionDispatcher( this,
                                                                ActionDispatcher.DISPATCH_FLAVOR);
         public ActionForward execute(ActionMapping mapping,
                                                                 ActionForm form,
                                                                 HttpServletRequest request,
                                                                 HttpServletResponse response)
                 throws Exception {
System.out.println( "execute() 执行了");
                 return dispatcher.execute(mapping, form, request, response);

        }

 

难道在DispatchAction中该方法可有可无吗？