[DRP]-EL表达式
E L（Expression Language） 目的：为了使JSP写起来更加简单。表达式语言的灵感来自于 ECMAScript 和 XPath 表达式语言，它提供了在 JSP 中简化表达式的方法，让Jsp的代码更加简化。
index 页面：目的，连接servelet类加载数据，然后转发页面。
<a href="servlet/JstlElServlet">测试EL表达式</a><br>
JstlElServlet 类：
package com.bjpowernode.jstl; import java.io.IOException; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * 测试el表达式 * @author Administrator * */ public class JstlElServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //普通字符串 request.setAttribute("hello", "Hello World"); //结构 Group group = new Group(); group.setName("动力节点603班"); User user = new User(); user.setUsername("张三"); user.setAge(23); user.setGroup(group); request.setAttribute("user", user); //map Map map = new HashMap(); map.put("k1", "v1"); map.put("k2", "v2"); request.setAttribute("map", map); //字符串数组 String[] strArray = new String[]{"a", "b", "c"}; request.setAttribute("str_array", strArray); //对象数组 User[] users = new User[10]; for (int i=0; i<users.length; i++) { users[i] = new User(); users[i].setUsername("张三_" + i); } request.setAttribute("users", users); //list List userList = new ArrayList(); for (int i=0; i<10; i++) { User usr = new User(); usr.setUsername("李四_" + i); userList.add(usr); } request.setAttribute("userList", userList); //empty request.setAttribute("v2", ""); request.setAttribute("v3", new ArrayList()); request.setAttribute("v4", "12345"); request.setAttribute("v5", null); request.getRequestDispatcher("/jstl_el.jsp").forward(request, response); } }
Group类：
package com.bjpowernode.jstl; public class Group { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } }
user类：
package com.bjpowernode.jstl; public class User { private String username; private int age; private Group group; public Group getGroup() { return group; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public void setGroup(Group group) { this.group = group; } }
jstl_el.jsp页面：
<%@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=GB18030"> <title>Insert title here</title> </head> <body> <h1>测试EL表达式</h1> <hr> <li>普通字符串</li><br> hello(jsp脚本):<%=request.getAttribute("hello") %><br> hello(el表达式，语法：$和{}):${hello }<br> hello(el表达式，el的内置对象pageScope,requestScope,sessionScope,applicationScope)<br> 如果不指定范围，它的搜索顺序为pageScope~applicationScope):${requestScope.hello }<br> hello(el表达式，指定范围从session取得):${sessionScope.hello }<br> <p> <li>结构,采用.进行导航，或称为存取器</li><br> 姓名：${user.username }<br> 年龄：${user.age }<br> 所属组：${user.group.name }<br> <p> <li>map</li><br> map.k1:${map.k1 }<br> map.k2:${map.k2 }<br> <p> <li>字符串数组，采用[]下标</li><br> strArray[1]:${str_array[1] }<br> <p> <li>对象数组，采用[]下标</li><br> users[5].username:${users[5].username }<br> <p> <li>list，采用[]下标</li><br> userList[6].username:${userList[6].username }<br> <p> <li>el表达式对运算符的支持</li><br> 1+1=${1+1 }<br> 10/5=${10/5 }<br> 10 div 5=${10 div 5 }<br> 10 % 3=${10 % 3 }<br> 10 mod 3 = ${ 10 mod 3 }<br> <!-- ==/eq !=/ne </lt >/gt &&/and ||/or !/not //div %/mod --> <p> <li>测试empty</li><br> v1:${empty v1}<br> v2:${empty v2}<br> v3:${empty v3}<br> v4:${empty v4}<br> v5:${empty v5}<br> </body> </html>
感觉和session 、cookie 的作用差不多，但是EL表达式只是后台先前台页面传值。数据不能共享！
让自己越来越优秀！
