jsp中的四种对象作用域

page：当前页面，也就是只要挑到别的页面就失效了，可以近似理解为java的this对象

request：一次会话，简单的理解就是一次请求范围内有效，例如如果通过forward方式跳转，则forward目标页面仍然可以拿到request中的属性值，再例如如果通过redirect方式进行页面跳转，由于redirect相当于重新发出的请求，request中的值会消失

session：浏览器进程，只要当前页面没有被关闭（没有被浏览器强制清除），不管怎么跳转都是有效的（也可以说是存在一个会话周期中）

application：服务器，只要服务器没有重启（没有被程序强制清除），数据就有效

pageScope.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<!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>

<body>

<%

//设置两个page范围的数据key->value

pageContext.setAttribute("name","page_barry");

pageContext.setAttribute("age",21);

%>

<%

//取值

String name=(String)pageContext.getAttribute("name");

int age=(Integer)pageContext.getAttribute("age");

%>

<font>姓 名:<%=name %></font>

<font>年 龄:<%=age %></font>

</body>

</html>

pageContext01.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<%@ page errorPage="error.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>

<%

pageContext.setAttribute("name0","pageInfo");

request.setAttribute("name1","requestInfo");

session.setAttribute("name2","sessionInfo");

application.setAttribute("name3","applicationInfo");

out.println("使用pageContext<br/>");

out.println("page中的属性值:"+pageContext.getAttribute("name0")+"<br/>");

out.println("request中的属性值:"+pageContext.getRequest().getAttribute("name1")+"<br/>");

out.println("session中的属性值:"+pageContext.getSession().getAttribute("name2")+"<br/>");

out.println("application中的属性值:"+pageContext.getServletContext().getAttribute("name3")+"<br/>");

%>

</body>

</html>

pageScope_2.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<!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>

<body>

<%

//设置两个page范围的数据key->value

pageContext.setAttribute("name","page_barry");

pageContext.setAttribute("age",21);

%>

<jsp:forward page="pageTarget_2.jsp"></jsp:forward>

</body>

</html>

pageTarget_2.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<!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>

<body>

<%

//取值

String name=(String)pageContext.getAttribute("name");

int age=(Integer)pageContext.getAttribute("age");

%>

<font>姓 名:<%=name %></font>

<font>年 龄:<%=age %></font>

</body>

</html>

requestScope.jsp

<%@ 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>

<%

//设置两个request范围的数据key->value

request.setAttribute("name","request_barry");

request.setAttribute("age",12);

%>

<jsp:forward page="requestTarget.jsp"></jsp:forward>

</body>

</html>

requestTarget.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<!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>

<%

//取值

String name=(String)request.getAttribute("name");

int age=(Integer)request.getAttribute("age");

//获取头信息

Enumeration enu=request.getHeaderNames();

while(enu.hasMoreElements()){

String headerName=(String)enu.nextElement();

String headerValue=request.getHeader(headerName);

%>

<h4><%=headerName %>&nbsp;<%=headerValue %></h4>

<%

}

%>

<font>姓名<%=name %></font><br>

<font>年龄<%=age %></font>

</body>

</html>

requestScope_2.jsp

<%@ 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>

<%

//设置两个request范围的数据key->value

request.setAttribute("name","request_barry");

request.setAttribute("age",12);

%>

<%response.sendRedirect("requestTarget_2"); %>

</body>

</html>

requestTarget_2.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<%@ page import="java.util.*" %>

<!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>

<%

//取值

String name=(String)request.getAttribute("name");

int age=(Integer)request.getAttribute("age");

//获取头信息

Enumeration enu=request.getHeaderNames();

while(enu.hasMoreElements()){

String headerName=(String)enu.nextElement();

String headerValue=request.getHeader(headerName);

%>

<h4><%=headerName %>&nbsp;<%=headerValue %></h4>

<%

}

%>

<font>姓名<%=name %></font><br>

<font>年龄<%=age %></font>

</body>

</html>

sessionScope.jsp

<%@ 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>

<%

//设置两个session范围的数据key->value

session.setAttribute("name","session_barry");

session.setAttribute("age",12);

%>

<h1>session值设置完毕！</h1>

</body>

</html>

sessionTarget.jsp

<%@ 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>

<%

String name=(String)session.getAttribute("name");

Integer age=(Integer)session.getAttribute("age");

%>

<font>姓名<%=name %></font><br>

<font>年龄<%=age %></font>

</body>

</html>

applicationScope.jsp

<%@ 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>

<%

//设置两个application范围的数据key->value

application.setAttribute("name","application_barry");

application.setAttribute("age",12);

%>

<h1>application值设置完毕！</h1>

</body>

</html>

applicationTarget.jsp

<%@ 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>

<%

//取值

String name=(String)application.getAttribute("name");

int age=(Integer)application.getAttribute("age");

%>

<font>姓名<%=name %></font><br>

<font>年龄<%=age %></font>

</body>

</html>

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原文地址：https://www.cnblogs.com/daochong/p/4824811.html