EL基础语法

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+"/";
%>

"-//W3C//DTD HTML 4.01 Transitional//EN">

  
    <base href="<%=basePath%>">
    
        
    
  
  
  
  <%
      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}
  
1、EL表达式从哪里取值？一般情况下，从作用域对象中取值

  ${a} ----${aaa} ---- ${age} ---- ${name}
  
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）

  ${uuu.nickname} ---- ${u2.address.district} ----${fruits[2]} ---- ${person1.address.city}
  
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

  ${xxx}
  
4、EL从指定作用域中取值？pageScope、requestScope、sessionScope、applicationScope

  ${pageScope.xxx} ---- ${requestScope.xxx} ---- ${sessionScope.xxx } ---- ${applicationScope.xxx}
  
5、EL表达式还可以取请求参数中的值：param、paramValues

  ${param.username} ---- ${paramValues.fav[2]}
  
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

  ${uuu["nickname"]} ---- ${param.type} ---- ${uuu[param.type]}
  
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

  ${empty a1} ---- ${empty a2} ---- ${empty a3} ---- ${empty a4}
  
8、EL表达式可以进行一些基本的数学运算

  ${
         5+4} ---- ${
        5-4} ---- ${
        5*4} ----${
        5/4} ---- ${
        5%4} ----${
        5+"4"}
  
9、EL表达式可以进行一些逻辑判断

  ${
         5>4} ---- ${
        5==4} ---- ${
        5 eq 4} --- ${uu1==uu2} --- ${uu1 eq uu2} ---- ${score==99}
  

 

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

转载于:https://www.cnblogs.com/cqming/p/10864130.html