Java Web学习笔记之---EL和JSTL
（一）EL
（1）EL作用
Expression Language（表达式语言），目的是代替JSP页面中复杂的代码
（2）EL表达式
${变量名}
（3）EL实现
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form action="ELServlet" method="post">
用户名：<input type="text" name="user">
密码：<input type="text" name="password">
<input type="submit">
</form>
</body>
</html>
ELServlet.java
package servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/ELServlet")
public class ELServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取输入值
String user=req.getParameter("user");
String password=req.getParameter("password");
//存入request
req.setAttribute("user",user);
req.setAttribute("password",password);
//转发至1.jsp
req.getRequestDispatcher("1.jsp").forward(req,resp);
}
}
1.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@page isELIgnored="false" %>
<html>
<head>
<title>Title</title>
</head>
<body>
用户名：${user}
密码：${password}
</body>
</html>
（二）JSTL
（1）JSTL介绍
JSP标准标签库
（2）与EL表达式的关系
JSTL通常与EL表达式一起实现JSP页面编码
（3）JSTL使用准备
在JSP页面添加
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
在pom.xml中配置
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
<version>1.2</version>
</dependency>
（4）JSTL常用标签
1.通用标签：set，out，remove
2.条件标签：if，choose
3.迭代标签：forEach
（5）常用标签的使用
JstlServlet.java
package servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@WebServlet("/JstlServlet")
public class JstlServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//创建Map集合，并存入数据
Map<String,Object> m1=new HashMap<String,Object>();
m1.put("user","AA");
m1.put("password","123");
m1.put("age","11");
Map<String,Object> m2=new HashMap<String,Object>();
m2.put("user","BB");
m2.put("password","123");
m2.put("age","12");
//将Map集合存入List集合
List<Map<String,Object>> list=new ArrayList<Map<String,Object>>();
list.add(m1);
list.add(m2);
//将List集合存入request中
req.setAttribute("list",list);
//转发
req.getRequestDispatcher("2.jsp").forward(req,resp);
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
}
2.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@page isELIgnored="false" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<html>
<head>
<title>Title</title>
</head>
<body>
<!-- 1.set标签：将值保存到指定范围内
2.将value值存到范围为scope的变量var中
-->
<c:set var="user" value="AA" scope="request"></c:set>
<c:set var="age" value="12" scope="request"></c:set>
<!-- out标签：将结果输出显示 -->
<c:out value="${user}"></c:out>
<!-- remove标签：删除指定域内数据 -->
<c:remove var="user"></c:remove>
<!-- if标签： test：放判断条件，如果条件为true，则输出标签体中的内容-->
<c:if test="${age==12}">
12岁
</c:if>
<!-- choose标签不能单独存在，内含when标签和otherwise标签，类似于if...else-->
<c:choose>
<c:when test="${age==12}">
是12岁
</c:when>
<c:otherwise>
不是12岁
</c:otherwise>
</c:choose>
<table>
<!-- forEach标签：类似于for（数据类型 变量名：集合或数组）
items中放集合或数组 var中放变量名
用变量名调用
-->
<c:forEach items="${list}" var="Map">
<tr>
<td>${Map.user}</td>
<td>${Map.password}</td>
<td>${Map.age}</td>
</tr>
</c:forEach>
</table>
</body>
</html>