el和jstl的区别

JSTL和EL表达式EL表达式
表达式语言（Expression Language），或称EL表达式，简称EL，是Java中的一种特殊的通用编程语言，借鉴于JavaScript和XPath。主要作用是在Java Web应用程序嵌入到网页（如JSP）中，用以访问页面的上下文以及不同作用域中的对象，取得对象属性的值，或执行简单的运算或判断操作。EL在得到某个数据时，会自动进行数据类型的转换。
表达式语法
${变量名}
使用时需要导入外部包，在tomcat服务器上找到此包，并导入。
apache-tomcat-8.5.34/lib/servlet-api.jar
案例从1.jsp 页面提交，通过servlet跳转到showEL.jsp页面完成赋值的输出
1.jsp
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>表单提交</title>
</head>
<body>
    <form action="<%=request.getContextPath() %>/ELServlet" method="post">
        用户名：<input type="text" name="username"><br>
        年龄： <input type="text" name="age"><br>
        <input type="submit" value="提交">
    </form>
 
     
</body>
</html>

ELServlet
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
package com.alan.controller;
 
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
 
@WebServlet("/ELServlet")
public class ELServlet extends HttpServlet {
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1、首先获取username和age的属性值
        String username = request.getParameter("username");
        String age = request.getParameter("age");
        //2、将其保存到request域中
        request.setAttribute("username", username);
        request.setAttribute("age", age);
        //3、跳转到showEL.jsp页面，我们通过EL表达式取出request域中的值
        request.getRequestDispatcher("/showEL.jsp").forward(request, response);
         
 
    }
 
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
 
    }
 
}

showEL.jsp
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>提交后页面</title>
</head>
<body>
        用户名：${username} <br>
        年龄：${age}
 
</body>
</html>
JSTL
JSP标准标签库（JSP Standard Tag Library）是Java EE网络应用程序开发平台的组成部分。它在JSP规范的基础上，扩充了一个JSP的标签库来完成一些通用任务，比如XML数据处理、条件执行、数据库访问、循环和国际化。
需要导入此jar包
jsp页面导入<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
JSTL标签介绍
通用标签 set out remove
条件标签 if choose
迭代标签 forEach
案例1
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 
 
    <!-- set、out、remove标签 -->
    <!-- set标签主要往指定的域中存放数据 -->
    <c:set var="user" value="张三" scope="request"></c:set>
    <!-- 将数据打印输出 -->
    <c:out value="${user}"></c:out>
    <!-- remove标签 -->
    <c:remove var="user" scope="request" />
    <c:out value="${user}"></c:out>
    <!--
    if标签
        test:按判断的条件,如果条件为true,执行标签体中的内容
         
     -->
    <c:set var="age" value="12" scope="request"></c:set>
    <c:if test="${age==11}">
        您的年龄为12岁
    </c:if>
    <hr>
    <!-- choose标签 -->
    <c:set var="age1" value="13" scope="request"></c:set>
    <c:choose>
        <c:when test="${age1==12}">
                您的年龄为12岁
        </c:when>
        <c:otherwise>
                您的年龄不是12岁
        </c:otherwise>
    </c:choose>
 
 
 
</body>
</html>

案例2 foreach
servelet
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
package com.alan.controller;
 
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.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
 
 
 
@WebServlet("/JSTLELServlet")
public class JSTLELServlet extends HttpServlet {
 
 
     
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         
        //1、将输入存入List中
        Map<String,Object> dataMap1 =  new HashMap<>();
        dataMap1.put("shopName", "联想笔记本");
        dataMap1.put("address", "北京");
        dataMap1.put("price", "4999");
        Map<String,Object> dataMap2 =  new HashMap<>();
        dataMap2.put("shopName", "神州笔记本");
        dataMap2.put("address", "南京");
        dataMap2.put("price", "3999");
        Map<String,Object> dataMap3 =  new HashMap<>();
        dataMap3.put("shopName", "小米笔记本");
        dataMap3.put("address", "深圳");
        dataMap3.put("price", "5999");
         
        List<Map<String,Object>> dataList = new ArrayList<>();
        dataList.add(dataMap1);
        dataList.add(dataMap2);
        dataList.add(dataMap3);
         
        //2、将List赋值到request的作用域中
        request.setAttribute("list", dataList);
        //3、在jsp页面取出List
        request.getRequestDispatcher("/2.jsp").forward(request, response);
     
    }
 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
 
}

jsp
[Java] 纯文本查看 复制代码
?
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
 
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>通过JSTL+EL表达式迭代List集合</title>
</head>
<body>
 
    <table border="1" cellspacing="0" >
        <tr>
            <td>商品名称</td>
            <td>产地</td>
            <td>价格</td>
        </tr>
        <c:forEach items="${list}" var="map">
            <tr>
                <td>${map.shopName }</td>
                <td>${map.address }</td>
                <td>${map.price}</td>
            </tr>
        </c:forEach>
    </table>
posted @ 2020-04-07 10:17  幽暗森林之猪大屁  阅读(493)  评论(0)    收藏  举报