• JSP内置对象 属性范围

    JSP内置对象概览

    内置对象概览
    NO 内置对象 类型 描述
    1 pageContext javax.servlet.jsp.PageContext JSP页面容器
    2 request javax.servlet.http.HttpServletRequest 得到用户的请求信息
    3 response javax.servlet.http.HttpServletResponse 服务器向客户端的回应信息
    4 session javax.servlet.http.HttpSession 用来保存每一个用户的信息
    5 application javax.servlet.ServletContext 表示所有用户的共享信息
    6 config javax.servlet.ServletConfig 服务器配置,可以得到初始化参数
    7 out javax.servlet.jsp.JspWriter 页面输出
    8 page java.lang.Object 表示从该页面生成的一个servlet实例
    9 exception java.lang.Throwable 表示JSP页面发生的异常,错误页有效

    JSP 4种属性范围

      1.page:只在一个页面中保存属性,跳转后失效.

      2.request:只在一次请求中保存,服务器跳转后依然有效

      3.session:在一次会话范围中,无论何种跳转都可以使用,但是新开的浏览器无法使用.

      4.application:在整个服务器上保存,所有用户都可以使用.

        page属性(pageContext)

           

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>get and set pageContext Attribute</title>
 9 </head>
10 <body>
11 <%//设置页面属性,该属性仅在本页有效
12     pageContext.setAttribute("name", "hx");
13     pageContext.setAttribute("birthday",new Date());
14 %>
15 <%//获得页面属性,并向下转型
16     String name = (String)pageContext.getAttribute("name");
17     Date d = (Date) pageContext.getAttribute("birthday");
18 %>
19 <%//显示页面属性值
20     out.println(name);
21     out.println(d);
22 %>
23 
24 </body>
25 </html>

        在本页中正常显示.修改使其发生服务器跳转.

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>get and set pageContext Attribute</title>
 9 </head>
10 <body>
11 <%//设置页面属性,该属性仅在本页有效
12     pageContext.setAttribute("name", "hx");
13     pageContext.setAttribute("birthday",new Date());
14 %>
15 <%//获得页面属性,并向下转型
16     String name = (String)pageContext.getAttribute("name");
17     Date d = (Date) pageContext.getAttribute("birthday");
18 %>
19 <%//显示页面属性值
20     out.println(name);
21     out.println(d);
22 %>
23 <jsp:forward page="2getAndSetPageAttribute.jsp"/>
24 
25 </body>
26 </html>
     1 <!-- 2getAndSetPageAttribute.jsp -->
 2 
 3 <%@ page language="java" contentType="text/html; charset=UTF-8"
 4     pageEncoding="UTF-8"%>
 5 <%@ page import="java.util.*" %>
 6 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 7 <html>
 8 <head>
 9 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
10 <title>Insert title here</title>
11 </head>
12 <body>
13 <%//获得页面属性,并向下转型
14     String name = (String)pageContext.getAttribute("name");
15     Date d = (Date) pageContext.getAttribute("birthday");
16 %>
17 <%//显示页面属性值
18     out.println(name);
19     out.println(d);
20 %>
21 </body>
22 </html>

     在发生跳转后,name和d均为null,pageContext仅本页有效

    request属性范围

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>request attribute scope</title>
 9 </head>
10 <body>
11 <%
12 request.setAttribute("name", "hx");
13 request.setAttribute("birthday",new Date());
14 %>
15 <%
16 String name=(String)request.getAttribute("name");
17 Date d = (Date)request.getAttribute("birthday");
18 %>
19 <%
20 out.println(name);
21 out.println(d);
22 %>
23 </body>
24 </html>

     本页生效

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>request attribute scope</title>
 9 </head>
10 <body>
11 <%
12 request.setAttribute("name", "hx");
13 request.setAttribute("birthday",new Date());
14 %>
15 <%
16 String name=(String)request.getAttribute("name");
17 Date d = (Date)request.getAttribute("birthday");
18 %>
19 <%
20 out.println(name);
21 out.println(d);
22 %>
23 <jsp:forward page="request_scope2.jsp"></jsp:forward>
24 </body>
25 </html>
26 
27 request_scope2.jsp
28 <%@ page language="java" contentType="text/html; charset=UTF-8"
29     pageEncoding="UTF-8"%>
30 <%@ page import="java.util.*" %>
31 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
32 <html>
33 <head>
34 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
35 <title>Insert title here</title>
36 </head>
37 <body>
38 <%
39 String name=(String)request.getAttribute("name");
40 Date d = (Date)request.getAttribute("birthday");
41 %>
42 <%
43 out.println(name);
44 out.println(d);
45 %>
46 </body>
47 </html>

     服务器跳转生效

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>request attribute scope</title>
 9 </head>
10 <body>
11 <%
12 request.setAttribute("name", "hx");
13 request.setAttribute("birthday",new Date());
14 %>
15 <%
16 String name=(String)request.getAttribute("name");
17 Date d = (Date)request.getAttribute("birthday");
18 %>
19 <%
20 out.println(name);
21 out.println(d);
22 %>
23 <a href="request_scope2.jsp">客户端跳转</a>
24 </body>
25 </html>
26 
27 
28 request_scope2.jsp
29 
30 <%@ page language="java" contentType="text/html; charset=UTF-8"
31     pageEncoding="UTF-8"%>
32 <%@ page import="java.util.*" %>
33 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
34 <html>
35 <head>
36 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
37 <title>Insert title here</title>
38 </head>
39 <body>
40 <%
41 String name=(String)request.getAttribute("name");
42 Date d = (Date)request.getAttribute("birthday");
43 %>
44 <%
45 out.println(name);
46 out.println(d);
47 %>
48 </body>
49 </html>

     使用超连接(客户端跳转后)属性值无效.

    session属性范围

     1 <%@ page language="java" contentType="text/html; charset=UTF-8"
 2     pageEncoding="UTF-8"%>
 3 <%@ page import="java.util.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 8 <title>Insert title here</title>
 9 </head>
10 <body>
11 <%
12     session.setAttribute("name", "hx");
13     session.setAttribute("birthday",new Date());
14 %>
15 <%
16     String name = (String)session.getAttribute("name");
17     Date d = (Date)session.getAttribute("birthday");
18 %>
19 <%
20     out.println(name);
21     out.println(d);
22 %>
23 
24 </body>
25 </html>

     

     本页有效

    <%@ 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>
<%
    session.setAttribute("name", "hx");
    session.setAttribute("birthday",new Date());
%>
<%
    String name = (String)session.getAttribute("name");
    Date d = (Date)session.getAttribute("birthday");
%>
<%
    out.println(name);
    out.println(d);
%>
<a href="session_scope2.jsp">test session scope</a>
</body>
</html>

session_scope2.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>
<%
    String name = (String)session.getAttribute("name");
    Date d = (Date)session.getAttribute("birthday");
%>
<%
    out.println(name);
    out.println(d);
%>
</body>
</html>

     客户端转发也有效

    application

    <%@ 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>
<%
    application.setAttribute("name", "hx");
    application.setAttribute("birthday",new Date());
%>
<%
    String name = (String)application.getAttribute("name");
    Date d = (Date)application.getAttribute("birthday");
%>
<%
    out.println(name);
    out.println(d);
%>
<a href="applicaion_scope2.jsp">test application scope</a>
</body>
</html>
    <%@ 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>
<%
    String name = (String)application.getAttribute("name");
    Date d = (Date)application.getAttribute("birthday");
%>
<%
    out.println(name);
    out.println(d);
%>
</body>
</html>

     在A浏览器中访问第一段代码所在URL,然后在B浏览器中访问第二段代码所在URL,显示正常

    重访PageContext:

        在page.setAttribute()方法是一个重写方法.

             一个是public void setAttribute(String name, Object value)

             一个是public void setAttribute(String name, Object value, int scope)

                     在此方法中的int scope相当于选择范围,可选的数为

                                 1.public void final int PAGE_SCOPE;                      表示page属性范围

                                 2.public void final int REQUEST_SCOPE;               表示request属性范围

                                 3.public void final int SESSION_SCOPE;                 表示session属性范围

                                 4.public void final int APPLICATION_SCOPE;         表示application属性范围

           pageContext对象可以随意设置属性范围,默认为page属性,而其他操作是对这一功能的包装.习惯上仅让pageContext具有page属性范围
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  • 原文地址：https://www.cnblogs.com/slowalker-lee/p/7894913.html
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