• EL&JSTL：JSTL总结

    目录：

    （1）set标签使用1

    （2）set标签和EL的表达式联合使用

    （3）if标签

    （4）choose标签 相当于多个判断语句

    （5）forEach循环

     （6）forEach遍历List集合

     （7）forEach遍历Map集合

     

    JSTL:披着标签的java工具类，java命令变成标签的形式，来满足需求，不让java命令落在jsp上

    为了jsp页面中看不见java代码，替换原来在jsp页面中的<% java代码%>，一个标签相当于一个java命令

    产生你原因：

    Java命令不能落在jsp上面去，所以把java命令披上一个标签，封装成一个标签使用

    另一个是EL表达式功能过于弱小

     

     

    创建04Model导入响应的jar包：

     

     

    （1）set标签使用1

     index.jsp:

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: DELL
    4.   Date: 2022/7/20
    5.   Time: 7:11
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <%--需要加jstl的标签--%>
    10. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    11.  
    12. set scope="application" var="sid" value="10">set>
    13. set scope="session" var="sname" value="mike">set>
    14. set scope="request" var="sage" value="26">set>
    15. set scope="page" var="home" value="上海">set>
    16.  
    17. 学员编号：${applicationScope.sid}
    18. 学员姓名：${sessionScope.sname}
    19. 学员年龄：${requestScope.sage}
    20. 学员籍贯：${pageScope.home}

    （2）set标签和EL的表达式联合使用

     index_2.jsp:

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: DELL
    4.   Date: 2022/7/20
    5.   Time: 8:19
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <%--需要加jstl的标签--%>
    10. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    11.  
    12. <%--设置用户今年的年龄--%>
    13. set scope="request" var="age" value="20">set>
    14.  
    15. <%--设置用户两年之后的年龄
    16.        执行顺序，限制性EL表达式，再执行JSTL，EL表达式先从request客户端读取数据+2，
    17.        然后并没有写到响应体中，而是写到value属性中，然后再执行set标签，
    18.        把request作用域中的20更新为22
    19. --%>
    20. set scope="request" var="age" value="${requestScope.age+2}">set>
    21.  
    22. 两年之后的年龄：${age}

    （3）if标签

      

    index_3.jsp:

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: DELL
    4.   Date: 2022/7/20
    5.   Time: 8:19
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <%--需要加jstl的标签--%>
    10. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    11.  
    12. <c:set scope="request" var="age" value="23">c:set>
    13.  
    14.  
    15. <c:if test="${sessionScope.age ge 18}">
    16.     <font color="red">欢迎光临font>
    17. c:if>
    18.  
    19. <c:if test="${sessionScope.age lt 18}">
    20.     <font color="red">过两年再来font>
    21. c:if>

    在运行项目的时候报了500：

     

    JSTL标签库报500错误解决方案

    原因分析
    Tomcat缺少jstl-api-1.2.jar和standard-1.1.2.jar和这两个jar包。

    解决方案
    将jstl-api-1.2.jar和standard-1.1.2.jar这两个包放入到D:\Program\apache-tomcat-8.0.53\lib目录下

    加入之后正常运行： 

     

    （4）choose标签 相当于多个判断语句

    index_4.jsp:

     

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: DELL
    4.   Date: 2022/7/20
    5.   Time: 9:18
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <%--需要加jstl的标签--%>
    10. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    11.  
    12. <c:set scope="page" var="salary" value="15000"></c:set>
    13. <c:choose>
    14.     <c:when test="${salary ge 50000}">高工资</c:when>
    15.     <c:when test="${salary ge 20000}">正常工资</c:when>
    16.     <c:when test="${salary ge 10000}">低工资</c:when>
    17.     <c:otherwise>不正常工资</c:otherwise>
    18. </c:choose>

     

     （5）forEach循环

     index_5.jsp:

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: DELL
    4.   Date: 2022/7/20
    5.   Time: 9:42
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <%--需要加jstl的标签--%>
    10. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    11.  
    12. <select>
    13.     <%
    14.         for (int i=1;i<=5;i++){
    15.     %>
    16.            <option>第<%=i%>页option>
    17.     <%
    18.         }
    19.     %>
    20. select>
    21.  
    22. <hr>
    23. JSTL语法替换上方的java语句<br>
    24. <select>
    25.     <c:forEach var="i" begin="1" end="5" step="1">
    26.         <option>第${pageScope.i}页option>
    27.     c:forEach>
    28. select>

     

     （6）forEach遍历List集合

     

     Student类：

    1. package com.bjpowernode.model;
    2.  
    3. public class Student {
    4.     private Integer sid;
    5.     private String sname;
    6.  
    7.     public Student(Integer sid, String sname) {
    8.         this.sid = sid;
    9.         this.sname = sname;
    10.     }
    11.  
    12.     public Integer getSid() {
    13.         return sid;
    14.     }
    15.  
    16.     public void setSid(Integer sid) {
    17.         this.sid = sid;
    18.     }
    19.  
    20.     public String getSname() {
    21.         return sname;
    22.     }
    23.  
    24.     public void setSname(String sname) {
    25.         this.sname = sname;
    26.     }
    27. }

    创建Servlet：SixServlet：

    1. package com.bjpowernode.controller;
    2.  
    3. import com.bjpowernode.model.Student;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.http.HttpServlet;
    7. import javax.servlet.http.HttpServletRequest;
    8. import javax.servlet.http.HttpServletResponse;
    9. import java.io.IOException;
    10. import java.util.ArrayList;
    11. import java.util.List;
    12.  
    13. public class SixServlet extends HttpServlet {
    14.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    15.  
    16.     }
    17.  
    18.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    19.         Student stu=new Student(10,"mike");
    20.         Student stu2=new Student(20,"allen");
    21.  
    22.         List list=new ArrayList();
    23.         list.add(stu);
    24.         list.add(stu2);
    25.  
    26.         request.setAttribute("key",list);
    27.         request.getRequestDispatcher("/index_6.jsp").forward(request,response);
    28.     }
    29. }

     在web.xml:中指定访问方式：

    2. <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    4.          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    5.          version="4.0">
    6.     
    7.     <servlet>
    8.         <servlet-name>SixServletservlet-name>
    9.         <servlet-class>com.bjpowernode.controller.SixServletservlet-class>
    10.     servlet>
    11.     <servlet-mapping>
    12.         <servlet-name>SixServletservlet-name>
    13.         <url-pattern>/six.dourl-pattern>
    14.     servlet-mapping>
    15.     
    16. web-app>

    index_6.jsp:

    1. <%@ page import="java.util.List" %>
    2. <%@ page import="com.bjpowernode.model.Student" %><%--
    3.   Created by IntelliJ IDEA.
    4.   User: DELL
    5.   Date: 2022/7/20
    6.   Time: 10:11
    7.   To change this template use File | Settings | File Templates.
    8. --%>
    9. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    10. <%
    11.     String path = request.getContextPath();
    12.     String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
    13. %>
    14. <%--需要加jstl的标签--%>
    15. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    16.  
    17. <html>
    18. <head>
    19.     <title>Titletitle>
    20.     <base href="<%=basePath%>">
    21. head>
    22. <body>
    23.   java命令获取数据<br>
    24.   <table border="2">
    25.       <tr>
    26.           <td>学员编号td>
    27.           <td>学员姓名td>
    28.       tr>
    29.       <%
    30.           List stuList=(List)request.getAttribute("key");
    31.           for(Student stu:stuList){
    32.       %>
    33.            <tr>
    34.                <td><%=stu.getSid()%>td>
    35.                <td><%=stu.getSname()%>td>
    36.            tr>
    37.       <%
    38.           }
    39.       %>
    40.   table>
    41. <hr>
    42. 通过JSTL标签来获取数据显示<br>
    43.     <table border="2">
    44.         <tr>
    45.             <td>学员编号td>
    46.             <td>学员姓名td>
    47.         tr>
    48.  
    49.         <c:forEach items="${requestScope.key}" var="stu">
    50.             <tr>
    51.                 <td>${stu.sid}td>
    52.                 <td>${stu.sname}td>
    53.             tr>
    54.         c:forEach>
    55.     table>
    56. body>
    57. html>

     

     （7）forEach遍历Map集合

    控制器：SixServlet:

    1. package com.bjpowernode.controller;
    2.  
    3. import com.bjpowernode.model.Student;
    4.  
    5. import javax.servlet.ServletException;
    6. import javax.servlet.http.HttpServlet;
    7. import javax.servlet.http.HttpServletRequest;
    8. import javax.servlet.http.HttpServletResponse;
    9. import java.io.IOException;
    10. import java.util.ArrayList;
    11. import java.util.HashMap;
    12. import java.util.List;
    13. import java.util.Map;
    14.  
    15. public class SixServlet extends HttpServlet {
    16.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    17.  
    18.     }
    19.  
    20.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    21.         Student stu=new Student(10,"mike");
    22.         Student stu2=new Student(20,"allen");
    23.  
    24.         //List集合
    25.         List list=new ArrayList();
    26.         list.add(stu);
    27.         list.add(stu2);
    28.  
    29.         //Map集合
    30.         Map map=new HashMap();
    31.         map.put("一班",stu);
    32.         map.put("二班",stu2);
    33.         request.setAttribute("mapKey",map);
    34.  
    35.         request.setAttribute("key",list);
    36.         request.getRequestDispatcher("/index_6.jsp").forward(request,response);
    37.     }
    38. }

    index_6.jsp:

    1. <%@ page import="java.util.List" %>
    2. <%@ page import="com.bjpowernode.model.Student" %><%--
    3.   Created by IntelliJ IDEA.
    4.   User: DELL
    5.   Date: 2022/7/20
    6.   Time: 10:11
    7.   To change this template use File | Settings | File Templates.
    8. --%>
    9. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    10. <%
    11.     String path = request.getContextPath();
    12.     String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
    13. %>
    14. <%--需要加jstl的标签--%>
    15. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    16.  
    17. <html>
    18. <head>
    19.     <title>Titletitle>
    20.     <base href="<%=basePath%>">
    21. head>
    22. <body>
    23.   java命令获取数据<br>
    24.   <table border="2">
    25.       <tr>
    26.           <td>学员编号td>
    27.           <td>学员姓名td>
    28.       tr>
    29.       <%
    30.           List stuList=(List)request.getAttribute("key");
    31.           for(Student stu:stuList){
    32.       %>
    33.            <tr>
    34.                <td><%=stu.getSid()%>td>
    35.                <td><%=stu.getSname()%>td>
    36.            tr>
    37.       <%
    38.           }
    39.       %>
    40.   table>
    41. <hr>
    42. 通过JSTL标签来获取数据显示<br>
    43.     <table border="2">
    44.         <tr>
    45.             <td>学员编号td>
    46.             <td>学员姓名td>
    47.         tr>
    48.  
    49.         <c:forEach items="${requestScope.key}" var="stu">
    50.             <tr>
    51.                 <td>${stu.sid}td>
    52.                 <td>${stu.sname}td>
    53.             tr>
    54.         c:forEach>
    55.     table>
    56.  
    57. <hr>
    58. <h1>遍历map集合h1>
    59.     <table border="2">
    60.         <tr>
    61.             <td>班级名称td>
    62.             <td>学员编号td>
    63.             <td>学员名称td>
    64.         tr>
    65.  
    66.         <%--遍历Map集合每次从Map集合中得到的是一个【键值对】
    67.             再把【键值对】交给循环变量
    68.             循环变量.key获得【键值对】中关键字名字 班级名称
    69.             循环变量.value 获得【键值对】中的内容 stu对象
    70.         --%>
    71.         <c:forEach items="${mapKey}" var="key_Value">
    72.             <tr>
    73.                 <td>${key_Value.key}td>
    74.                 <td>${key_Value.value.sid}td>
    75.                 <td>${key_Value.value.sname}td>
    76.             tr>
    77.         c:forEach>
    78.     table>
    79. body>
    80. html>

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  • 原文地址：https://blog.csdn.net/dengfengling999/article/details/125884427