Struts标签库

     在JSP页面中，使用标记库代替传统的Java代码来实现页面的显示逻辑是大势所趋，然而，由于自定义标记很容易造成重复定义和非标准的实现，于是出现了基于java Web的JSTL和基于struts的taglib等标签库来解决这些问题。

  这些标签库在实现原理上相差无几，学会一种，另一种也就很容易上手，那咱们就从Struts的标签库走起。

  常用的strust标签库有<bean:write>、<logic:empty>和<logic:notEmpty>、<logic:present>和<logic:notPresent>、<logic:iterator>4种。

  使用方法：

  1.在strus-config.xml中配置message-resources，注意，这个标签要放在action-mappings标签后面。配置信息如下：

<message-resources parameter="MessageResources" />

    2.在src目录下引入提供国际化资源文件MessageResources.properties

  3.在JSP页面中引入taglib

<%@ taglib uri="http://struts.apache.org/tags-bean" prefix="bean"%> <%@ taglib uri="http://struts.apache.org/tags-logic" prefix="logic"%>

        4.下面是分别是<bean:wriete>（获取字段值、JavaBean属性值）、<logic:empty>和<logic:notEmpty>（判断是否为空）、<logic:present>和<logic:notPresent>（判断是否存在）、<logic:iterator>（迭代取出集合中的数据）分别在Action和JSP页面的配置

   (1)<bean:wriete>-->action

public class BeanWriteAction extends Action {@Overridepublic ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request, HttpServletResponse response)throws Exception {// 普通字符串request.setAttribute("hello", "quwenzhe");request.setAttribute("today", new Date());Group group = new Group();group.setName("提高班");User user = new User();user.setUsername("quwenzhe");user.setAge("24");user.setGroup(group);request.setAttribute("user", user);return mapping.findForward("success");}}

           <bean:wriete>-->JSP

姓名：<input type="text" name="username" value="<bean:write name="user" property="username"/>"><br/>年龄：<input type="text" name="age" value="<bean:write name="user" property="age"/>"><br>所属组:<input type="text" name="group" value="<bean:write name="user" property="group.name"/>"><br/>

       (2)<logic:empty>和<logic:notEmpty>、<logic:present>和<logic:notPresent>-->action

public class EmptyPresentAction extends Action {@Overridepublic ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request, HttpServletResponse response)throws Exception {request.setAttribute("attr1", null);request.setAttribute("attr2", "");request.setAttribute("attr3", new ArrayList());return mapping.findForward("success");}}

             <logic:empty>和<logic:notEmpty>、<logic:present>和<logic:notPresent>-->JSP

<p><logic:empty name="attr1">attr1为空</logic:empty><logic:notEmpty name="attr1">attr1为空</logic:notEmpty><logic:present name="attr1">attr1存在</logic:present><logic:notPresent name="attr1">attr1不存在</logic:notPresent></p><p><logic:empty name="attr2">attr2为空</logic:empty><logic:notEmpty name="attr2">attr2为空</logic:notEmpty><logic:present name="attr2">attr2存在</logic:present><logic:notPresent name="attr2">attr2不存在</logic:notPresent></p><p><logic:empty name="attr3">attr3为空</logic:empty><logic:notEmpty name="attr3">attr3为空</logic:notEmpty><logic:present name="attr3">attr3存在</logic:present><logic:notPresent name="attr3">attr3不存在</logic:notPresent></p>

           (3)<logic:iterator>-->action

public class IteratorAction extends Action {@Overridepublic ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request, HttpServletResponse response)throws Exception {Group group = new Group();group.setName("提高班");List userList = new ArrayList();for (int i = 0; i < 10; i++) {User user = new User();user.setUsername("quwenzhe-->" + i);user.setAge("24-->" + i);user.setGroup(group);userList.add(user);}request.setAttribute("userList", userList);return mapping.findForward("success");}}

              <logic:iterator>-->JSP

<table border="1"><tr><td>姓名</td><td>年龄</td><td>所属组</td></tr><logic:empty name="userList"><tr><td colspan="3">没有符合条件的数据</td></tr></logic:empty><logic:notEmpty name="userList"><logic:iterate id="user" name="userList"><tr><td><bean:write name="user" property="username"/></td><td><bean:write name="user" property="age"/></td><td><bean:write name="user" property="group.name"/></td></tr></logic:iterate></logic:notEmpty></table>

        这样我们在后台Action中通过request设置的值，在JSP页面中通过标签就能很方便的获取到，大大提高工作效率。