EL built-in objects
In EL expressions, objects that can be used without creation are called EL hidden (implicit, built-in) objects. There are a total of 11 hidden objects in EL, and they are all similar to Map. 10 of them are Map and one is PageContext
parameter hidden object
l param: param is of type Map<String, String>! The param object can be used to get parameters, the same as the request.getParameter() method.
request.getParameter("username"); if then null then this result is null
And: param.username If it is empty then the return is an empty string ""
Single value accepts:
<form action="/jsp_demo/login.jsp" method="post">
name:<input name="username">
password:<input name="password" type="password">
<input type="submit" value="提交">
</form>
<h1>${param.username }</h1>
<h1>${param.password }</h1>
Multiple values are accepted:
<h1>${paramValues.favor[0] } , ${paramValues.favor[1] }</h1>
Get header information
<!-- Get header information-->
<h1>${header.host }</h1>
cookie settings
<!-- cookie acquisition-->
<!-- Set cookies first -->
<%
response.addCookie(new Cookie("personName","houzi"));
%>
<!-- Get header information-->
<h2>${cookie.personName.name } : ${cookie.personName.value }</h2>
pageScope gets the object in the domain
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!-- import package -->
<%@ page import="cn.wgg.jsp.*" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<%
//create person object
Person person = new Person();
person.setAge(20);
person.setName("houzi");
person.setID(1);
pageContext.setAttribute("person", person);
%>
<!-- pageScope takes value from field-->
<h2>${pageScope.person.name }</h2>
<h2>${pageScope.person.age }</h2>
<h2>${pageScope.person.ID }</h2>
<!-- Get header information-->
<!-- Get header information-->
</body>
</html>