结识EL
简单介绍下EL的常用形式，继续用程序说明：
package com.keith.el;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.struts.action.Action;import org.apache.struts.action.ActionForm;import org.apache.struts.action.ActionForward;import org.apache.struts.action.ActionMapping;import com.keith.taglibs.Group;import com.keith.taglibs.User;public class ElAction extends Action {@Overridepublic ActionForward execute(ActionMapping mapping, ActionForm form,HttpServletRequest request, HttpServletResponse response)throws Exception {// 字符串request.setAttribute("he", "hello EL ");// 结构Group group = new Group();group.setGroupName("KEITH的朋友");User user = new User();user.setName("keith");user.setAge(19);user.setGroup(group);request.setAttribute("user", user);// mapMap mapValue = new HashMap();mapValue.put("key1", "value1");mapValue.put("key2", "value2");request.setAttribute("mapValue", mapValue);// 字符串数组String[] strArray = new String[] { "a", "b", "c" };request.setAttribute("strArray", strArray);// 对象数组User[] user1 = new User[10];for (int i = 0; i < 10; i++) {User u = new User();u.setName("U_" + i);user1[i] = u;}request.setAttribute("user1", user1);//listList userList = new ArrayList();for (int i = 0; i < 10; i++) {User u_list = new User();u_list.setName("u_list"+i);userList.add(u_list);} // 测试${empty }request.setAttribute("value2", "");request.setAttribute("value3", "abcd");request.setAttribute("value4", new ArrayList());? request.setAttribute("userList", userList);return mapping.findForward("elTest");}}?用到了User类：
package com.keith.taglibs;public class User {private String name;private int age;private Group group;public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}Group类：
package com.keith.taglibs;public class Group {private String groupName;public String getGroupName() {return groupName;}public void setGroupName(String groupName) {this.groupName = groupName;}}?struts-config.xml:
<action-mappings><action path="/elTest"type="com.keith.el.ElAction"><forward name="elTest" path="/elTest.jsp"></forward></action><action-mappings>
?elTest.jsp页面：由于用到了logic标签所以引入下：
<%@ taglib prefix="logic" uri="http://struts.apache.org/tags-logic"%>
?elTest.jsp:
<body><h2>EL表达式TEST</h2><h3>EL(输出字符串)</h3>${he }<hr><h3>EL(输出结构)</h3><table><tr><td>姓名</td><td>年龄</td><td>班级</td></tr><logic:empty name="user"><font color="red">user不存在</font></logic:empty><logic:notEmpty name="user"><tr><td>${user.name }</td><td>${user.age }</td><td>${user.group.groupName }</td></tr></logic:notEmpty></table><hr><h3>EL(输出MAP)</h3>mapValue.key1的值是:${mapValue.key1 }<br />mapValue.key2的值是:${mapValue.key2 }<br /><hr /><h3>EL(输出字符串数组)</h3>strArray[1]的值:${strArray[1] }<br />strArray[2]的值:${strArray[2] }<br /><hr /><h3>EL(输出对象数组)</h3>user1[1].name:${user1[1].name }<hr /><h3>EL(list输出数组)</h3>userList[1].name:${userList[1].name }<hr/><h3>EL表达式计算</h3>1+9=${1+9 }<br/>1-9=${1-9 }<br/>1*9=${1*9 }<br/>1/9=${1/9 }<br/> <h3>测试EL{empty}</h3>value1:${empty value1 }<br/>value2:${empty value2 }<br/>value3:${empty value3 }<br/>value4:${empty value4 }<br/></body>?很简单............