EventDispatchAction作用:
用于处理多个提交动作的EventDispatchAction类。这个类也是DispatchAction的子类,它在使用上要比LookupDispatchAction类容易的多。EventDispatchAction类的基本原理是通过<action>元素的parameter属性指定多个动作,中间用逗号(,)分隔。每个动作实际上就是<html:submit>标签的property属性值。这样EventDispatchAction类就可以根据每个<html:submit>标签的属性值来确定用户按的是哪个提交按钮了。
 
【第1步】实现EventDispatchAction的子类
/*
* $Id: EventDispatchActionExample.java 471754 2006-11-06 14:55:09Z husted $
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements.    See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership.    The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License.    You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
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* software distributed under the License is distributed on an
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package org.apache.struts.webapp.dispatch;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.actions.EventDispatchAction;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;

/**
* Example EventDispatchAction.
*
* @version $Rev: 471754 $ $Date: 2006-11-06 08:55:09 -0600 (Mon, 06 Nov 2006) $
*/

public class EventDispatchActionExample extends EventDispatchAction {

        private int fooCount;
        private int barCount;

        /**
         * Example "foo" method.
         *
         * @param mapping The ActionMapping used to select this instance
         * @param form The optional ActionForm bean for this request
         * @param request The servlet request we are processing
         * @param response The servlet response we are creating
         *
         * @exception Exception if business logic throws an exception
         */

        public ActionForward doFoo(ActionMapping mapping,
                                                             ActionForm form,
                                                             HttpServletRequest request,
                                                             HttpServletResponse response)
                throws Exception {

                fooCount++;

                ActionMessages messages = new ActionMessages();
                messages.add("foo", new ActionMessage("count.foo.message", fooCount+""));
                saveMessages(request, messages);

                return (mapping.findForward("success"));

        }

        /**
         * Example "bar" method.
         *
         * @param mapping The ActionMapping used to select this instance
         * @param form The optional ActionForm bean for this request
         * @param request The servlet request we are processing
         * @param response The servlet response we are creating
         *
         * @exception Exception if business logic throws an exception
         */

        public ActionForward doBar(ActionMapping mapping,
                                                             ActionForm form,
                                                             HttpServletRequest request,
                                                             HttpServletResponse response)
                throws Exception {
                barCount++;

                ActionMessages messages = new ActionMessages();
                messages.add("bar", new ActionMessage("count.bar.message", barCount+""));
                saveMessages(request, messages);

                return (mapping.findForward("success"));

        }

}
 
有两个方法:doFoo和doBar,分别用来处理property属性值为“doFoo”和“doBar”的<html:submit>标签提交的请求动作
 
  【第2步】配置EventDispatchAction类
<action path="/eventAction-default"    
                                type="org.apache.struts.webapp.dispatch.EventDispatchActionExample"
                                parameter="doFoo,bar=doBar,default=doBar"
                                name="testForm"
                                scope="request">
                        <forward name="success" path="/eventAction.jsp"/>
                </action>
 
parameter="doFoo,bar=doBar,default=doBar"
如果submit标签不提供property 或者提供了property值,在Action中找不到相关的方法对应时,会提交的default标记的doBar方法中
【第3步】实现有多个提交按钮的JSP页面
                 <html:form action="eventAction-default" style="display:inline">
                            <html:submit property="doFoo"><bean:message key="button.foo.label" /></html:submit>
                    </html:form>
                             
                    <html:form action="eventAction-default" style="display:inline">
                     <input type="hidden" name="Method" value="doBar" />
                            <html:submit><bean:message key="button.bar.label" /></html:submit>
                    </html:form>
                             
                    <html:form action="eventAction-default" style="display:inline">
                            <html:submit><bean:message key="button.default.label" /></html:submit>
                    </html:form>
 
 
运行结果:
 <html:submit><bean:message key="button.default.label" /></html:submit>,会执行default 指向的方法。如果没有default,会报
ServletException: Request[/eventAction-submit] does not contain handler parameter.
2.如果在配置文件中有相关的方法声明比如parameter="missingMethod",但是在Action java文件中却没有missingMethod()方法的实现,会报
NoSuchMethodException: Action[/eventAction-error] does not contain specified method (check logs)
3. 也不能在配置文件总使用方法名execcute 。否则:
ServletException: Do not use 'execute' or 'perform' with DispatchAction.
4.如果忘记了在配置文件中,为Action设置parameter属性,会报:
ServletException: DispatchMapping[/eventAction-noparam] does not define a handler property