Article Directory
一、THE
Case presentation
(1) Read saved information with EL
Create a Java Enterprise project - ELJSTLDemo 
Click the [Finish] button 
to modify the Artifact name 
Redeploy the project Modify 
the home page 
Start the server and view the results 
Create the net.huawei.servlet package and create the ServletDemo01 class in the package
package net.huawei.servlet;
import javax.servlet.RequestDispatcher;
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;
/**
* 功能：保存request属性，请求转发到指定页面
* 作者：华卫
* 日期：2023年04月20日
*/
@WebServlet(name = "ServletDemo01", urlPatterns = "/demo01")
public class ServletDemo01 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 保存request属性
request.setAttribute("username", "无心剑");
request.setAttribute("password", "903213");
// 获取请求转发器，转发到`demo01.jsp`页面
RequestDispatcher dispatcher = request.getRequestDispatcher("/demo01.jsp");
// 请求转发
dispatcher.forward(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
}
Create the demo01.jsp page in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>demo01</title>
</head>
<body>
使用JSP表达式获取属性：<br />
用户名：<%=request.getAttribute("username")%> <br />
密码：<%=request.getAttribute("password")%> <br />
<hr />
使用EL获取属性：<br />
用户名：${username} <br />
密码：${password} <br />
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo01
pageContext object
pageContext object case
Create a demo02.jsp file in the web directory to demonstrate the usage of the pageContext implicit object
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>demo02 - 演示pageContext对象</title>
</head>
<body>
请求URI为：${pageContext.request.requestURI} <br />
Content-Type响应头：${pageContext.response.contentType} <br />
服务器信息：${pageContext.servletContext.serverInfo} <br />
Servlet注册名：${pageContext.servletConfig.servletName} <br />
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo02.jsp
Web domain related object example
Create a demo03.jsp file in the web directory to demonstrate how these 4 implicit objects access the properties in the JSP domain object
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>demo03 - 演示Web域相关对象</title>
</head>
<body>
<% pageContext.setAttribute("userName", "无心剑"); %>
<% request.setAttribute("bookName", "动态网站开发"); %>
<% session.setAttribute("userName", "陈燕文"); %>
<% application.setAttribute("bookName", "大数据实时处理"); %>
表达式\${pageScope.userName}的值为：${pageScope.userName} <br />
表达式\${requestScope.bookName}的值为：${requestScope.bookName} <br />
表达式\${sessionScope.userName}的值为：${sessionScope.userName} <br />
表达式\${applicationScope.bookName}的值为：${applicationScope.bookName} <br />
表达式\${userName}的值为：${userName}
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo03.jsp
Implicit object for accessing environment information
Case demonstration Obtaining the request parameters passed by the client
Create a demo04.jsp file in the web directory to demonstrate the request parameters passed by the client
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>demo04 - 演示获取客户端传递的请求参数</title>
</head>
<body style="text-align: center;">
<form action="${pageContext.request.contextPath}/demo04.jsp">
num1：<input type="text" name="num1"><br />
num2：<input type="text" name="num"><br />
num3：<input type="text" name="num"><br /> <br />
<input type="submit" value="提交" />
<input type="submit" value="重置" /><hr />
num1： ${param.num1} <br />
num2： ${paramValues.num[0]} <br />
num3： ${paramValues.num[1]} <br />
</form>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo04.jsp, 
enter three numbers in the form above, which are 100, 200, and 300, and click the submit button
Cookie object
Cookie object case
Create a demo05.jsp file in the web directory to demonstrate how to obtain the information in the Cookie object.
Start the server and visit http://localhost:8080/ELJSTLDemo/demo05.jsp. Since it is the first time the browser visits the demo05.jsp page, the server has not received the cookie information named userName at this time, so the information of the Cookie object will not be displayed in the browser window.
Refresh the page to see the result
initParam object
initParam object case
Set web application initialization parameters in web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<context-param>
<param-name>author</param-name>
<param-value>无心剑</param-value>
</context-param>
</web-app>
Create a demo06.jsp file in the web directory to demonstrate the acquisition of Web application initialization parameters through the initParam object
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>demo06 - 演示通过initParam对象获取Web应用初始化参数</title>
</head>
<body>
Web应用初始化参数author的值：${initParam.author}
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo06.jsp
3. JSTL
Import the JSTL package
Create a lib directory in WEB-INF, copy the two files jstl.jar and standard.jar to the lib directory,
add jstl.jar and standard.jar to the project as a library, 
and click the [OK] button
Case Demo Tag Library
Create demo07.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<html>
<head>
<title>demo07 - 演示标签库</title>
</head>
<body>
<h1 style="color: red; text-align: center">
<c:out value="欢迎访问泸州职业技术学院~"/>
</h1>
<jsp:useBean id="now" class="java.util.Date" />
<h3 style="text-align: center">
<fmt:formatDate value="${now}" pattern="yyyy年MM月dd日 HH:mm:ss" />
</h3>
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo07.jsp
4. Core tag library in JSTL
<c:out> tag example
Case 1. Demo default attribute
Create demo08.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo08 - 演示default属性</title>
</head>
<body>
<%--第1个out标签 --%>
userName属性的值：
<c:out value="${param.username}" default="用户名未知"/> <br />
<%--第2个out标签 --%>
userName属性的值：
<c:out value="${param.username}">
用户名未知
</c:out>
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo08.jsp
Case 2. Demonstration of the escapeXML attribute
The <c:out> tag has an important attribute escapeXml, which can convert special characters into HTML code before outputting. A case demonstrates how to use the escapeXml attribute to convert special characters.
Create demo09.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo09 - 演示escapeXml属性</title>
</head>
<body>
<c:out value="${param.username}" escapeXml="false">
<meta http-equiv="refresh" content="0;url=http://www.lzy.edu.cn" />
</c:out>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo09.jsp 
start the server, visit http://localhost:8080/ELJSTLDemo/demo09.jsp
Example of <c:remove> tag
Create demo10.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo10 - 演示移除标签</title>
</head>
<body>
<%
pageContext.setAttribute("username", "无心剑");
session.setAttribute("username", "陈燕文");
%>
<c:remove var="username" scope="page"/>
用户名：<c:out value="${username}"/>
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo10.jsp
<c:if> tag example
Create demo11.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo11 - 演示单分支标签</title>
</head>
<body>
<c:set value="1" var="visitCount" />
<c:if test="${visitCount==1}">
<h3 style="text-align: center">你第一次访问~欢迎访问泸职院~</h3>
</c:if>
</body>
</html>
Start the server and visit http://localhost:8080/ELJSTLDemo/demo11.jsp
) for three label cases
Create demo12.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo12 - 演示多分支标签</title>
</head>
<body>
<c:choose>
<c:when test="${empty param.username}">
未知用户~
</c:when>
<c:when test="${param.username=='无心剑'}">
${param.username}是教师~
</c:when>
<c:otherwise>
${param.username}是学生~
</c:otherwise>
</c:choose>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo12.jsp 
visit http://localhost:8080/ELJSTLDemo/demo12.jsp?username=Wuxinjian 
visit http://localhost:8080/ELJSTLDemo/demo12.jsp?username=Chen Yanwen
<c:forEach> tag example
Create demo13.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page import="java.util.HashMap" %>
<%@ page import="java.util.Map" %>
<html>
<head>
<title>demo13 - 演示循环标签</title>
</head>
<body>
<%
String[] fruits = {"苹果", "橘子", "葡萄", "香蕉"};
%>
String数组中的元素：
<c:forEach var="name" items="<%=fruits%>">
${name}
</c:forEach>
<br />
<%
Map userMap = new HashMap();
userMap.put("01", "北京");
userMap.put("02", "上海");
userMap.put("03", "广州");
%>
HashMap集合中的元素：
<c:forEach var="entry" items="<%=userMap%>">
${entry.key} : ${entry.value}
</c:forEach>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo13.jsp 
and create demo14.jsp in the web directory
<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.List" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo14 - 演示循环标签</title>
</head>
<body>
colorsList集合（指定迭代范围和步长）：
<%
List colorsList=new ArrayList();
colorsList.add("red");
colorsList.add("yellow");
colorsList.add("blue");
colorsList.add("green");
colorsList.add("black");
%>
<c:forEach var="color" items="<%=colorsList%>"
begin="1" end="3" step="2">
${color}
</c:forEach>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo14.jsp
Example of URL-related tags
Create demo15.jsp in the web directory
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>demo15 - 演示URL相关标签</title>
</head>
<body>
使用绝对路径构造URL：
<c:url var="myURL" value="http://localhost:8080/ELJSTLDemo/demo08.jsp">
<c:param name="username" value="陈燕文" />
</c:url>
<a href="${myURL}">demo08.jsp</a><br />
使用相对路径构造URL：
<c:url var="myURL" value="demo08.jsp?username=无心剑" />
<a href="${myURL}">demo08.jsp</a>
</body>
</html>
Start the server, visit http://localhost:8080/ELJSTLDemo/demo15.jsp 
and click the first hyperlink 
Return to the previous page 
Return to the previous page