<%-- <%@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>