2020-3-6 seo達(dá)人
一.有關(guān)于內(nèi)置對(duì)象的作用域
主要說(shuō)明2個(gè)對(duì)象，request，session
1、request 對(duì)象
request 對(duì)象是 javax.servlet.httpServletRequest類(lèi)型的對(duì)象。 該對(duì)象代表了客戶(hù)端的請(qǐng)求信息，主要用于接受通過(guò)HTTP協(xié)議傳送到服務(wù)器的數(shù)據(jù)。（包括頭信息、系統(tǒng)信息、請(qǐng)求方式以及請(qǐng)求參數(shù)等）。
request只在2個(gè)頁(yè)面之間傳遞，每一次新的請(qǐng)求都會(huì)新建一個(gè)request對(duì)象，也就是說(shuō)可能會(huì)request對(duì)象不一致導(dǎo)致空指針異常。
2、session 對(duì)象
session 對(duì)象是由服務(wù)器自動(dòng)創(chuàng)建的與用戶(hù)請(qǐng)求相關(guān)的對(duì)象。服務(wù)器為每個(gè)用戶(hù)都生成一個(gè)session對(duì)象，用于保存該用戶(hù)的信息，跟蹤用戶(hù)的操作狀態(tài)。session對(duì)象內(nèi)部使用Map類(lèi)來(lái)保存數(shù)據(jù)，因此保存數(shù)據(jù)的格式為 “Key/value”。 session對(duì)象的value可以使復(fù)雜的對(duì)象類(lèi)型，而不僅僅局限于字符串類(lèi)型。
session對(duì)象在整個(gè)會(huì)話只有一個(gè)，也就是說(shuō)session對(duì)象的數(shù)據(jù)會(huì)一直保留直到主動(dòng)進(jìn)行數(shù)據(jù)更改。
二.表單提交
在index.jsp中使用form進(jìn)行數(shù)據(jù)的提交，action的目標(biāo)是check.jsp，method是post
三.驗(yàn)證跳轉(zhuǎn)
當(dāng)form提交信息后交給check.jsp驗(yàn)證，使用getParameter來(lái)得到form的信息，并使用setAttribute保存。在check.jsp中判斷賬號(hào)密碼是否正確后，使用
<jsp:forward page=".jsp"></jsp:forward>
1
進(jìn)行跳轉(zhuǎn)，.jsp是想要跳轉(zhuǎn)的頁(yè)面路徑。
四.詳細(xì)代碼
index.jsp
<%@ page language="java" import="java.util." pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>登陸</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="check.jsp" method="post">
請(qǐng)輸入用戶(hù)名：
<input type = "text" name = "username"><br/>
請(qǐng)輸入密碼：
<input type = "password" name = "passwd"><br/>
<input type="submit" name="submit" value="登錄">
</form>
</body>
</html>
check.jsp
<%@ page language="java" import="java.util." pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>驗(yàn)證</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%
String username = (String)request.getParameter("username");
String passwd = (String)request.getParameter("passwd");
request.setAttribute("username", username);
request.setAttribute("passwd", passwd);
if(username.equals("admin")&&passwd.equals("123")){
%>
<jsp:forward page="succeed.jsp"></jsp:forward>
<%}else{ %>
<jsp:forward page="failed.jsp"></jsp:forward>
<%} %>
</body>
</html>
succeed.jsp
<%@ page language="java" import="java.util." pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>登陸成功</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%
String username = (String)request.getAttribute("username");
String passwd = (String)request.getAttribute("passwd");
%>
<%=username %>登陸成功
</body>
</html>
failed.jsp
<%@ page language="java" import="java.util." pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>登陸失敗</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%
String username = (String)request.getAttribute("username");
String passwd = (String)request.getAttribute("passwd");
%>
<%=username %>登陸失敗
</body>
</html>
五.注意事項(xiàng)
在jsp中使用form提交表單不能直接進(jìn)行跳轉(zhuǎn)，否則操作不慎就容易出現(xiàn)空指針異常，建議交由單獨(dú)的跳轉(zhuǎn)頁(yè)面處理
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