javaee之el表达式的运用

来源：互联网发布：cors网络账号怎么获取编辑：程序博客网时间：2024/06/08 06:43

一、关于el表达式的基本运算

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>el的基本语法</title>    <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>    <%    String name="狗娃";    //放入域对象中    session.setAttribute("name", name);     %>          <%=name %>     <hr/>          EL: ${name}          <%--     ${name}  等价于： pageContext.findAttribute("name")      --%>  </body></html>

<%@page import="gz.itcast.entity.Student"%><%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>EL获取不同类型的数据</title>    <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>    <!-- 1.字符串 -->    <%    String msg = "狗剩";    pageContext.setAttribute("msg", msg);     %>        ${msg}        <hr/>        <!-- 2.对象 -->    <%    Student student = new Student(1,"狗娃",20);    pageContext.setAttribute("stu", student);     %>    ${stu.age}   <%-- .age 代表调用getAge()方法 --%>        <hr/>    <!-- 3.List或数组集合 -->    <%    List<Student> list = new ArrayList<Student>();    list.add(new Student(1,"狗娃",20));    list.add(new Student(2,"狗剩",22));    list.add(new Student(3,"狗蛋",23));    pageContext.setAttribute("list", list);     %>    ${list[1].name}  <br/>${list[2].age }          <hr/>    <!-- 4.Map集合 -->    <%    Map<String,Student> map = new HashMap<String,Student>();    map.put("s1", new Student(1,"肉丝",20));    map.put("s2", new Student(2,"露丝",22));    map.put("s3", new Student(3,"夹克",24));    pageContext.setAttribute("map", map);     %>          ${map['s1'].name}<br/><%--建议使用这种语法 --%>     ${map.s1.name } <%-- .s1  key的内容必须是字符串 --%>  </body></html>

<%@page import="gz.itcast.entity.Student"%><%@ page language="java" import="java.util.*" pageEncoding="UTF-8" isELIgnored="false"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>EL运算</title>    <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>    <%--算术 --%>    ${10+4 }<br/>    ${10*4 }<br/>    ${10/2 }        <hr/>        <%--比较 --%>    ${10>5 }<br/>    ${10<5 }<br/>    ${10==5 }<br/>        <hr/>    <%--逻辑 --%>    ${true&&true }<br/>    ${false&&true }<br/>    ${true||false }<br/>    ${!true}<br/>        <hr/>    <%--三目 --%>    ${10>5?"成功":"失败"}        <%    //模拟后台数据    Student student = new Student();    student.setGender("女");        pageContext.setAttribute("student", student);     %>        性别：    <input type="radio" name="gender" value="男"  ${student.gender=="男"?"checked='checked'":""} />男    <input type="radio" name="gender" value="女"  ${student.gender=="女"?"checked='checked'":""}/>女            <hr/>    <%--判空 --%>    <%    String name="";    pageContext.setAttribute("name", name);     %>           判空： ${name==null || name==""}  判空：${empty name}         </body></html>

如果当使用el表达式的时候，需要把数据放进域对象中，因为el表达式的基本就是在域对象取出相对应name的数据，域对象包括：pageContext、request、session、ServletContext。

现在大多数的数据在页面显示都是通过el表达式的

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