String u = request.getParameter("url");当传入有url参数"url"时,字符串u 能显示正确的"url"值. 但是如果url参数中没有"url"时,u的值out.println(u);显示的是null.但是我将 u == null 和 u.equals(null)输出时,结果都是false.这是为什么啊?比如:访问bbs.jsp?url=abc时,将u输出可以显示abc.但是如果访问bbs.jsp时,将u输出显示null,但是将u == null 和 u.equals(null) 输出都是false.
<%@ page contentType="text/html;charset=GBK" language="java"
import="java.sql.*" errorPage=""%>
<%@ page pageEncoding="GB18030"%>
<%@ page import="java.sql.*,java.io.*,com.bbs1.bbs.*,java.util.*"%>
<%
request.setCharacterEncoding("GBK"); String action = request.getParameter("action");
String url = request.getParameter("url");
if (action != null && action.trim().equals("post")) { String userName = request.getParameter("username");
String userPassWord = request.getParameter("password"); Connection conn = null;
Statement stmt = null;
ResultSet rs = null; conn = DB.getConn();
stmt = DB.createStmt(conn);
String sql = "select * from users where username='" + userName
+ "'";
rs = DB.executeQuery(stmt, sql); if (rs.next() && userPassWord.equals(rs.getString("password"))) {
//out.println(null == url);
out.println(url.equals(null));
session.setAttribute("userName", userName);
//response.sendRedirect("ccutbbs.jsp");
} else {
out.println("登陆失败, 用户名或密码错误~~");
}
DB.close(rs);
DB.close(stmt);
DB.close(conn);
} else {
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3c.org/TR/1999/REC-html401-19991224/loose.dtd">
<!-- saved from url=(0045)http://www.pkucn.com/logging.php -->
<HTML xmlns="http://www.w3.org/1999/xhtml">
<HEAD>
<TITLE>工大计算机论坛 www.pkucn.com 致力于做中国最好的计算机学术论坛！ - Powered by
Discuz!</TITLE>
<META content="text/html; charset=gbk" http-equiv=Content-Type>
<META name=verify-v1
content=m+YHHMOgjvAYEaWK1vzTnyzibVPh3FurWGoNudSJjng=>
<META name=keywords content=工大,计算机,学术,论坛,学者,网络文学,原创,工大bbs,工大论坛,工大计算机论坛>
<META name=description
content=" 工大计算机论坛 www.pkucn.com 致力于做全球最好的计算机学术论坛！ - Discuz! Board">
<META name=GENERATOR content="MSHTML 8.00.6001.18783">
<META name=author content="Discuz! Team and Comsenz UI Team">
<META name=copyright content="2001-2007 Comsenz Inc.">
<META name=MSSmartTagsPreventParsing content=True>
<META content=Yes http-equiv=MSThemeCompatible>
<LINK title="工大计算机论坛 www.pkucn.com" rel=archives
href="http://www.pkucn.com/archiver/">
<LINK rel=stylesheet type=text/css href="login_files/style_1.css">
<LINK rel=stylesheet type=text/css
href="forumdata/cache/style_1_append.css">
<SCRIPT type=text/javascript>var IMGDIR = 'images/default';var attackevasive = '0';var gid = 0;var fid = parseInt('0');var tid = parseInt('0');</SCRIPT> <SCRIPT type=text/javascript src="login_files/common.js"></SCRIPT> <SCRIPT type=text/javascript src="login_files/menu.js"></SCRIPT> <SCRIPT type=text/javascript src="login_files/ajax.js"></SCRIPT>
</HEAD>
<BODY onkeydown=if (event.keyCode==27)returnfalse;;>
<DIV id=append_parent></DIV>
<DIV id=ajaxwaitid></DIV>
<DIV class=wrap>
<DIV id=header>
<H2>
<A title="工大计算机论坛 www.pkucn.com"
href="http://www.pkucn.com/index.php"><IMG border=0
alt="工大计算机论坛 www.pkucn.com" src="login_files/logo.gif"> </A>
</H2>
<DIV id=ad_headerbanner></DIV>
</DIV>
<DIV id=menu>
<SPAN class=frameswitch> </SPAN>
<UL>
<LI>
<A class=notabs href="register.jsp">注册</A>
</LI>
<LI class=current>
<A href="login.jsp">登录</A>
</LI>
<LI>
<A href="http://www.pkucn.com/member.php?action=list">会员</A>
</LI>
<LI>
<A href="faq.jsp">帮助</A>
</LI>
</UL>
</DIV>
<DIV id=nav>
<A href="ccutbbs.jsp">工大计算机论坛 www.ccutbbs.com</A> » 会员登录
</DIV>
<FORM method=post name=login action="login.jsp">
<INPUT value="post" type=hidden name="action">
<INPUT value=<%=url %> type=hidden name="url">
<DIV class="mainbox formbox">
<SPAN class=headactions><A
href="http://www.pkucn.com/faq.php?action=message&id=3"
target=_blank>登录帮助</A> </SPAN>
<H1>
会员登录
</H1>
<TABLE cellSpacing=0 summary=会员登录 cellPadding=0>
<TBODY>
<TR>
<TH onclick=document.login.username.focus();>
<LABEL>
用户名
</LABEL> </TH>
<TD>
<INPUT id="username" maxLength=40 style="width:150px" name="username">
<A href="register.jsp">立即注册</A>
</TD>
</TR>
<TR>
<TH>
<LABEL for=password>
密码
</LABEL> </TH>
<TD>
<INPUT name="password" type="password" style="width:150px">
<A href="forgetpassword.jsp">忘记密码?</A> </TD>
</TR>
<TR>
<TH>
登录有效期
</TH>
<TD>
<LABEL>
<INPUT class=radio tabIndex=8 value=315360000 type=radio
name=cookietime>
永久
</LABEL>
<LABEL>
<INPUT class=radio tabIndex=9 value=2592000 type=radio
name=cookietime>
一个月
</LABEL>
<LABEL>
<INPUT class=radio tabIndex=10 value=86400 type=radio
name=cookietime>
一天
</LABEL>
<LABEL>
<INPUT class=radio tabIndex=11 value=3600 type=radio
name=cookietime>
一小时
</LABEL>
<LABEL>
<INPUT class=radio tabIndex=12 value=0 CHECKED type=radio
name=cookietime>
浏览器进程
</LABEL>
</TD>
</TR>
<TR>
<TH>
</TH>
<TD>
<BUTTON class=submit tabIndex=100 name=loginsubmit type=submit
value="true">
提交
</BUTTON>
</TD>
</TR>
</TBODY>
</TABLE>
</DIV>
</FORM>
<%-- 这个是一个判断时差是否超过24小时的代码--%>
<%-- <SCRIPT type=text/javascript>
document.login.username.focus();
var mydate = new Date();
var mytimestamp = parseInt(mydate.valueOf() / 1000);
if (Math.abs(mytimestamp - 1247721406) > 86400) {
window
.alert('注意:\n\n您本地计算机的时间设定与论坛时间相差超过 24 个小时，\n这可能会影响您的正常登录，请调整本地计算机设置。\n\n当前论坛时间是: (GMT +8) 2009-7-16 13:16\n如果您认为论坛时间不准确，请与论坛管理员联系。');
}
</SCRIPT>--%>
</DIV>
<DIV id=ad_footerbanner1></DIV>
<DIV id=ad_footerbanner2></DIV>
<DIV id=ad_footerbanner3></DIV>
</BODY>
<%
}
%>
</HTML>