重生day04-优快云博客

本文链接：https://blog.youkuaiyun.com/hellojava20170101/article/details/70911600

本文详细介绍了JavaBean的概念及实现方式，并深入探讨了EL表达式的原理与应用。通过具体的示例代码展示了如何在不同作用域中使用EL表达式获取JavaBean的属性值。

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javaBean,el表达式

javaBean说到底是一个类，

1、使用public修饰

2、公共的无参构造方法

3、包含属性的操作方法

el表达式，原理是pageContext里有个方法findAttribute()

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>
<%
	//pageContext.setAttribute("msg","pageContextValue");
	request.setAttribute("msg","requestValue");
	session.setAttribute("msg","sessionValue");
	application.setAttribute("msg","applicationValue");
%>
${msg}
</body>
</html>

el的内置对象或者叫隐式对象

使用eltest?username=xiao来访问就可以看到值

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>
username=${param.username}	
</body>
</html>

el内置对象的作用域，主要是用来获取不同作用域的值

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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>
<%
	pageContext.setAttribute("msg","pageContextValue");
	request.setAttribute("msg","requestValue");
	session.setAttribute("msg","sessionValue");
	application.setAttribute("msg","applicationValue");
%>
pageContext=${pageScope.msg}<br/>
request=${requestScope.msg}<br/>
session=${sessionScope.msg}<br/>
application=${applicationScope.msg}<br/>
</body>
</html>