javaee之el表达式的运用_:checked="profile?.gender === '男-优快云博客

本文链接：https://blog.youkuaiyun.com/css1223mjf/article/details/52075931

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