EL表达式

Expression Language
image.png
这个EL表达式挺神奇的有点类似于jQuery

  1. package cn.java.controller;
  3. import java.io.IOException;
  4. import javax.servlet.ServletException;
  5. import javax.servlet.annotation.WebServlet;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  10. /**
  11.  * Servlet implementation class ELServlet
  12.  */
  13. @WebServlet("/ELServlet")
  14. public class ELServlet extends HttpServlet {
  15.     private static final long serialVersionUID = 1L;
  17.     /**
  18.      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  19.      */
  20.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  21.         //1、首先获取username和age属性值
  22.         String username = request.getParameter("username");
  23.         String age = request.getParameter("age");
  24.         //2、将获取的数据保存到request域中
  25.         request.setAttribute("username", username);
  26.         request.setAttribute("age", age);
  27.         //3、跳转到2.jsp页面，通过EL表达式来取出request域中的数据
  28.         request.getRequestDispatcher("2.jsp").forward(request, response);
  30.     }
  33.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  34.         // TODO Auto-generated method stub
  35.         doGet(request, response);
  36.     }
  38. }

1.jsp

  1. <%@ page language="java" contentType="text/html; charset=utf-8"
  2.     pageEncoding="utf-8"%>
  3. <!DOCTYPE html>
  4. <html>
  5. <head>
  6. <meta charset="utf-8">
  7. <title>Insert title here</title>
  8. </head>
  9. <body>
  10.     <form action="<%=request.getContextPath() %>/ELServlet" method="post">
  11.         用户名: <input type = "text" name = "username"><br>
  12.         年龄:<input type = "text" name ="age"><br>
  13.         <input type="submit" value="提交">
  14.     </form>
  15. </body>
  16. </html>

2.jsp

  1. <%@ page language="java" contentType="text/html; charset=utf-8"
  2.     pageEncoding="utf-8"%>
  3. <!DOCTYPE html>
  4. <html>
  5. <head>
  6. <meta charset="utf-8">
  7. <title>通过EL表达式取数据</title>
  8. </head>
  9. <body>
  10.     姓名:${username}<br>
  11.     年龄:${age }
  12. </body>
  13. </html>

JSTL

JavaServerPages Standard Tag Library
image.png

image.png

通用标签image.png

image.png
scope代表域

  1. <%@ page language="java" contentType="text/html; charset=utf-8"
  2.     pageEncoding="utf-8"%>
  3. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
  4. <!DOCTYPE html>
  5. <html>
  6. <head>
  7. <meta charset="utf-8">
  8. <title>Insert title here</title>
  9. </head>
  10. <body>
  11.     <!-- set标签主要是王指定的域中存放数据 -->
  12.     <c:set var = "user" value = "张三" scope = "request"></c:set>
  14.     <!-- out标签将数据进行打印显示 -->
  15.     <c:out value = "${user}" ></c:out>
  17.     <hr>
  19.     <c:remove var="user" scope="request"/>
  21.     <hr>
  22.     <c:out value = "${user}" ></c:out>
  23. </body>
  24. </html>

以上jsp的显示：
image.png

条件标签

都有个test，test里面写判断条件

if

choose

choose需要配合when和otherwise使用

  1. <%@ page language="java" contentType="text/html; charset=utf-8"
  2.     pageEncoding="utf-8"%>
  3. <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
  4. <!DOCTYPE html>
  5. <html>
  6. <head>
  7. <meta charset="utf-8">
  8. <title>Insert title here</title>
  9. </head>
  10. <body>
  11.     <c:set var="age" value="13" scope="request"></c:set>
  12.     <!-- if标签
  13.         test：接判断的条件，如果提交为true，执行标签体内的内容
  14.      -->
  15.     <c:if test="${age == 12 }">
  17.         您的年龄为12岁。
  18.     </c:if>
  19.     Hello World~
  20.     <hr>
  21.     <c:choose>
  22.         <c:when test="${age == 12 }">
  23.             您的年龄为12岁。
  24.         </c:when>
  25.         <c:otherwise>
  26.             您的年龄不是12岁。
  27.         </c:otherwise>
  29.     </c:choose>
  32. </body>
  33. </html>

迭代标签

forEach