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EL基础语法 

<%--  <%@page import="javax.validation.constraints.Null"%>--%>
<%@page import="cn.sxt.model.Address"%>
<%@page import="cn.sxt.model.T_user"%>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ page isELIgnored="false" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>    
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
  </head>
  
  <body>
  <%
      int a = 10;
      
      //数据在四大作用域对象中
      pageContext.setAttribute("a",a);
      request.setAttribute("aaa", true);
      session.setAttribute("age", 18);
      application.setAttribute("name", "cqm");
      
      //简单对象
      T_user user = new T_user(1,"admin","admin","cqm");
      request.setAttribute("uuu", user);
      //复合对象
      T_user u2 = new T_user(2,"admin-cqm","123123","qm", new Address("广东省","广州市","天河区"));
      pageContext.setAttribute("u2", u2);
      //List中的数据
      List list = new ArrayList();
      list.add("apple");
      list.add("orange");
      list.add("watermelon");
      list.add("pineapple");
      pageContext.setAttribute("fruits", list);
      //Map中的数据
      Map map = new HashMap();
      map.put("name", "zhangsan");
      map.put("age", 18);
      map.put("gender", "女");
      map.put("address", new Address("广东省","广州市","天河区"));
      pageContext.setAttribute("person1", map);
      
      //作用域中有相同的key
      pageContext.setAttribute("xxx", "pageContext");
      request.setAttribute("xxx", "request");
      session.setAttribute("xxx", "session");
      application.setAttribute("xxx", "application");
      
      T_user uu1 = new T_user(5,"admin","admin","张三"); 
      T_user uu2 = new T_user(5,"admin","admin","张三"); 
      
      request.setAttribute("uu1", uu1);
      request.setAttribute("uu2", uu2);
      
      request.setAttribute("score", 99);
      
      pageContext.setAttribute("a1", null);
      pageContext.setAttribute("a2", new ArrayList());
      pageContext.setAttribute("a4", "");
      
  
  
   %>
  尚学堂教育系统，欢迎${user.nickname}
  <h3>1、EL表达式从哪里取值？一般情况下，从作用域对象中取值</h3>
  ${a} ----${aaa} ---- ${age} ---- ${name}
  <h3>2、EL表达式可以取什么类型的值？基本数据类型、引用数据类型（对象、复合对象、List、Map）</h3>
  ${uuu.nickname} ---- ${u2.address.district} ----${fruits[2]} ---- ${person1.address.city}
  <h3>3、EL表达式从哪个作用域中取值？默认从最小作用域中开始寻找，找不到往大的作用域中找，都找不到显示为空</h3>
  ${xxx}
  <h3>4、EL从指定作用域中取值？pageScope、requestScope、sessionScope、applicationScope</h3>
  ${pageScope.xxx} ---- ${requestScope.xxx} ---- ${sessionScope.xxx } ---- ${applicationScope.xxx}
  <h3>5、EL表达式还可以取请求参数中的值：param、paramValues</h3>
  ${param.username} ---- ${paramValues.fav[2]}
  <h3>6、EL表达式除了"."操作符之外，还有"[]"操作符："[]"可以解析子EL表达式</h3>
  ${uuu["nickname"]} ---- ${param.type} ---- ${uuu[param.type]}
  <h3>7、EL表达式中的为空判断：empty判断为空的有：空字符串、null、空集合、空map</h3>
  ${empty a1} ---- ${empty a2} ---- ${empty a3} ---- ${empty a4}
  <h3>8、EL表达式可以进行一些基本的数学运算</h3>
  ${5+4} ---- ${5-4} ---- ${5*4} ----${5/4} ---- ${5%4} ----${5+"4"}
  <h3>9、EL表达式可以进行一些逻辑判断</h3>
  ${5>4} ---- ${5==4} ---- ${5 eq 4} --- ${uu1==uu2} --- ${uu1 eq uu2} ---- ${score==99}
  </body>
</html>

 

posted on 2019-05-14 19:34  QM.C  阅读(279)  评论(0)    收藏  举报