EL表达式和JSTL标签快速入门
jsp代码：
<%@ page language="java" import="cn.itcast.domain.*,java.util.*" pageEncoding="UTF-8"%>
<%@page import="java.util.ArrayList"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>el表达式</title>
</head>
<body>
<!-- 数据以普通方式带来 -->
<%
String data = "abcd";
request.setAttribute("data",data);
%>
${data } <%-- pageContext.findAttribute("data") page request session application --%>
<br/>
<!-- 数据存在bean里面带来 -->
<%
Person p = new Person();
p.setName("aaaa");
request.setAttribute("person",p);
%>
${person.name }
<br/>
<!-- 数据存在复杂bean里面带来 -->
<%
Person p1 = new Person();
Address a = new Address();
a.setCity("上海");
p1.setAddress(a);
request.setAttribute("p1",p1);
%>
${p1.address.city }
<br/>
<!-- 数据存在List集合里面带来 -->
<%
List list = new ArrayList();
list.add(new Person("aaa"));
list.add(new Person("bbb"));
list.add(new Person("ccc"));
request.setAttribute("list",list);
%>
${list[1].name }
<br/>
<!-- 数据存在Map集合里面带来 -->
<%
Map map = new HashMap();
map.put("aa",new Person("aaaaa"));
map.put("bb",new Person("bbbbb"));
map.put("cc",new Person("ccccc"));
map.put("dd",new Person("ddddd"));
map.put("111",new Person("eeeee"));
request.setAttribute("map",map);
%>
${map.bb.name }
${map['111'].name } <%--用el表达式在取数据时，通常用.号，.号取不出来时，用[]--%>
<%-- 取得当前web应用的名称: /day09 ,用于web链接不写死--%>
${pageContext.request.contextPath }
<a href="${pageContext.request.contextPath }/index.jsp">点点</a>
</body>
</html>
JSP代码：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ page import="cn.itcast.domain.Person"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>使用jstl+el完成集合迭代</title>
</head>
<body>
<%
List list = new ArrayList();
list.add(new Person("aaa"));
list.add(new Person("bbb"));
list.add(new Person("ccc"));
request.setAttribute("list",list);
%>
<c:forEach var="person" items="${list}">
${person.name }<br/>
</c:forEach>
<br/>
<%
Map map = new HashMap();
map.put("aa",new Person("aaaaa"));
map.put("bb",new Person("bbbbb"));
map.put("cc",new Person("ccccc"));
map.put("dd",new Person("ddddd"));
map.put("111",new Person("eeeee"));
request.setAttribute("map",map);
%>
<c:forEach var="entry" items="${map}">
${entry.key } : ${entry.value.name}<br/>
</c:forEach>
//代表用户登录了
<c:if test="${user!=null}">
欢迎您：${user.username }
</c:if>
//代表用户没登录
<c:if test="${user==null">
用户名：<input type="text" name="username"/>
密码：<input type="password" name="password"/>
</c:if>
</body>
</html>
