我有一个带有jdbc连接的jsp页面，并且在第一次加载时它准确地显示了数据，但之后它显示了空表我认为第二次从内存而不是从服务器加载
我不知道背后的问题是什么
这里有详细信息
我有一个servlet，用于维护登录用户的会话，然后在创建会话后，servlet将用户重定向到jsp页面的视图页面，并在DB中显示现有记录
当servlet重定向页面时，jsp可以显示记录，但是当我从任何其他html页面访问此页面时，它无法显示记录，这里是要查看的jsp页面的代码。
<%@ page import="java.sql.ResultSet" %>
<%@ page import="java.math.BigDecimal" %>
<%@ page import="java.sql.SQLException" %>
<%@ page import="java.util.logging.Level" %>
<%@ page import="java.util.logging.Logger" %>
<%@ page import="iEHR.cDBProcessor" %>
<HTML>
<HEAD>
<TITLE>View Patient</TITLE>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=windows-1251">
<script type="text/javascript" language="javascript" src="datepicker/main.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/prototype-1.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/prototype-base-extensions.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/prototype-date-extensions.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/behaviour.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/ratingbar.js"></script>
<script type="text/javascript" language="javascript" src="datepicker/datepicker.js"></script>
<link rel="stylesheet" href="datepicker/datepicker.css">
<script type="text/javascript" language="javascript" src="datepicker/behaviors.js"></script>
<style type="text/css">
<!--
img {
border: none;
}
.tah10 {
font-family: "Times New Roman", Times, serif;
font-size: 14px;
text-decoration: none;
color: #000000;
font-style: italic;
}
.tah11 {
font-family: Tahoma;
font-size: 11px;
text-decoration: none;
color: #000000;
}
.ver10 {
font-family: Verdana, Arial, Helvetica, sans-serif;
font-size: 10px;
text-decoration: none;
color: #000000;
}
.ver11 {
font-family: Verdana, Arial, Helvetica, sans-serif;
font-size: 11px;
text-decoration: none;
color: #000000;
}
.tah9 {
font-family: Tahoma;
font-size: 9px;
text-decoration: none;
color: #000000;
}
.ver9 {
font-family: Verdana, Arial, Helvetica, sans-serif;
font-size: 9px;
text-decoration: none;
color: #000000;
}
td {
vertical-align: top;
color: 497B99;
font-size: 12px;
font-style: normal;
font-weight: bolder;
}
-->
</style>
<style type="text/css">
<!--
.bgtop {
background-repeat: repeat-x;
background-position: top;
}
-->
</style>
<style type="text/css">
<!--
a {
font-family: Times New Roman, Times, serif;
font-size: 12px;
font-weight: bolder;
color: 467B99;
text-decoration: none;
}
.datepicker{
font-family: Times New Roman, Times, serif;
font-size: 12px;
font-weight: bolder;
color: 467B99;
text-decoration: none;
}
a:hover {
font-size: 10px;
font-weight: bold;
color: FF8400;
}
.style1 {
color: 467B99;
font-family: Times New Roman, Times, serif;
font-size: 12px;
text-decoration: none;
font-style: normal;
font-weight: bolder;
}
.style2 {
font-family: Times New Roman, Times, serif;
font-size: 12px;
font-style: normal;
font-weight: bolder;
color: 467B99;
text-decoration: none;
}
-->
</style>
</HEAD>
<BODY BGCOLOR=#FFFFFF LEFTMARGIN=0 TOPMARGIN=0 MARGINWIDTH=0 MARGINHEIGHT=0>
<!-- ImageReady Slices (0005_red.psd - Slices: 03, 04, 05) -->
<TABLE WIDTH=100% height="100%" BORDER=0 CELLPADDING=0 CELLSPACING=0 bgcolor="#FFFFFF">
<TR>
<TD width="12%">
<TABLE WIDTH=159 BORDER=0 CELLPADDING=0 CELLSPACING=0>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/logo.gif" WIDTH=159 HEIGHT=128 ALT=""></TD>
</TR>
<TR>
<TD>
<IMG SRC="images/s1.gif" WIDTH=20 HEIGHT=20 ALT=""></TD>
<TD>
<A HREF="#">
<IMG SRC="images/r1.gif" WIDTH=29 HEIGHT=20 BORDER=0 ALT=""></A></TD>
<TD>
<A HREF="#">
<IMG SRC="images/r2.gif" WIDTH=31 HEIGHT=20 BORDER=0 ALT=""></A></TD>
<TD>
<A HREF="#">
<IMG SRC="images/r3.gif" WIDTH=31 HEIGHT=20 BORDER=0 ALT=""></A></TD>
<TD>
<A HREF="#">
<IMG SRC="images/r4.gif" WIDTH=28 HEIGHT=20 BORDER=0 ALT=""></A></TD>
<TD>
<IMG SRC="images/s2.gif" WIDTH=20 HEIGHT=20 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/s3.gif" WIDTH=159 HEIGHT=93 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/h1.jpg" WIDTH=159 HEIGHT=32 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/img1.jpg" WIDTH=159 HEIGHT=76 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/img2.jpg" WIDTH=159 HEIGHT=81 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6>
<IMG SRC="images/img3.jpg" WIDTH=159 HEIGHT=79 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=6> <IMG SRC="images/but1.jpg" ALT="" WIDTH=159 HEIGHT=42 border="0" usemap="#Map"></TD>
</TR>
</TABLE> </TD>
<TD width="12%">
<TABLE WIDTH=167 BORDER=0 CELLPADDING=0 CELLSPACING=0>
<TR>
<TD COLSPAN=2>
<IMG SRC="images/h2.jpg" WIDTH=167 HEIGHT=25 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg1.gif" HEIGHT=94>
<div style="padding:20;padding-top:5;padding-right:10;padding-bottom:0;color:ffffff" class="tah10">
<strong>Noesis</strong><br><br>
<strong>Inovative EHR Services </strong> <br>
<br>
</div> </TD>
</TR>
<TR>
<TD COLSPAN=2>
<IMG SRC="images/s4.jpg" WIDTH=167 HEIGHT=52 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg2.gif">
<div style="padding-left:0px;padding-top:12px;padding-bottom:2"><a href="AddPatient.jsp"><span style="padding-left:20;padding-top:5">Add Patient </span></a></div> </TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg3.gif" HEIGHT=18>
<div style="padding-left:20;padding-top:5"><a href="AddPastMedicalHistory.jsp">Add Patient History</a> </div>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg4.gif" HEIGHT=18>
<div style="padding-left:20;padding-top:5"><a href="AddPatientInsurance.jsp">Add Patient Insurance</a></div> </TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg5.gif" HEIGHT=18 >
<div style="padding-left:20;padding-top:5">View Patient Records</div></TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg6.gif" HEIGHT=18 >
<div style="padding-left:20;padding-top:5"><a href="#"></a><a href="AboutUs.jsp">About Us</a></div> </TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg7.gif" HEIGHT=18 >
<div style="padding-left:20;padding-top:5"><a href="#"></a><a href="ContactUs.jsp">Contact Us</a></div> </TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg8.gif" HEIGHT=18 >
<div style="padding-left:20;padding-top:5"><a href="#"></a></div> </TD>
</TR>
<TR>
<TD COLSPAN=2>
<IMG SRC="images/h3.gif" WIDTH=167 HEIGHT=65 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=2 background="images/bg9.gif" HEIGHT=94>
<div style="padding:15;padding-top:3;padding-bottom:3;color:737373" class="tah10"></div> </TD>
</TR>
<TR>
<TD COLSPAN=2>
<IMG SRC="images/h4.jpg" WIDTH=167 HEIGHT=41 ALT=""></TD>
</TR>
<TR>
<TD background="images/bg10.jpg" WIDTH=123 HEIGHT=32>
<div style="padding-left:15;padding-top:1">
<input name="text" type="text" size="11">
</div></TD>
<TD width="44"> <IMG SRC="images/but2.jpg" ALT="" WIDTH=44 HEIGHT=32 border="0" usemap="#Map2"></TD>
</TR>
<TR>
<TD COLSPAN=2>
<IMG SRC="images/s5.jpg" WIDTH=167 HEIGHT=48 ALT=""></TD>
</TR>
<TR>
<TD COLSPAN=2> </TD>
</TR>
</TABLE> </TD>
<TD width="72%">
<table width=100% height="193" border=0 cellpadding=0 cellspacing=0>
<tr>
<td height=172 colspan="4" ><span class="bgtop"><img src="images/f_m.jpg"></span></td>
<td height=172 colspan="2" width="63%" background="images/bg_tile_1.gif" class="bgtop"> </td>
</tr>
<tr>
<td height=19 colspan="4" background="images/bg11.gif" > </td>
</tr>
</table>
<%! private ResultSet rsResult; %>
<%! cDBProcessor DBProcess = new cDBProcessor(); %>
<%
DBProcess.ConnectTODB();
if(request.getAttribute("dbrec") != null)
{
rsResult = DBProcess.statement.executeQuery("SELECT * FROM patients");
}//end if
out.println("<table border=\"0\"><tr><td valign=\"top\" >");
out.println("<tr><th>Patient ID</th><th>First Name</th><th>Middle Name</th><th>Last Name</th><th>Gender</th><th>Marital Status</th><th>Phone No.</th><th>Address</th>");
out.println("<th>Date Of Birth</th><th>Last Date Of Exam</th><th>Status</th></tr>");
//data display on page
if(rsResult!= null)
{
try
{
while (rsResult.next())
{
BigDecimal bdPatientID = rsResult.getBigDecimal("patient_id");
String strFirstname = rsResult.getString("first_name");
String strLastname = rsResult.getString("last_name");
String strMiddlename = rsResult.getString("middle_name");
String strGeneder = rsResult.getString("gender");
String strMeritalStatus = rsResult.getString("marital_status");
BigDecimal bdPhoneNo = rsResult.getBigDecimal("phone_no");
String strAddress = rsResult.getString("address");
String strDOB = rsResult.getDate("birth_dt") == null ? "" : rsResult.getDate("birth_dt").toString();
String strDOE = rsResult.getDate("dt_of_exam") == null ? "" :rsResult.getDate("dt_of_exam").toString();
String strStatus;
Byte bPatientStatus= rsResult.getByte("status");
if(bPatientStatus == 1)
{
strStatus = "Active";
}//end if
else
{
strStatus = "Inactive";
}//end else
out.println("<tr><td>"+bdPatientID+"</td><td>"+strFirstname+"</td><td>"+strMiddlename+"</td><td>"+strLastname+"</td>");
out.println("<td>"+strGeneder+"</td><td>"+strMeritalStatus+"</td><td>"+bdPhoneNo+"</td><td>"+strAddress+"</td>");
out.println("<td>"+strDOB+"</td><td>"+strDOE+"</td><td>"+strStatus+"</td></tr>");
}//end while
out.println("</table>");
}//end try
catch (SQLException ex)
{
out.println("<I>exception</I><br>");
}//end catch
}//end if
DBProcess.CloseDB();
%>
</TD>
<TD width="4%" background="images/bg_tile_1.gif" class="bgtop"> </TD>
</TR>
<TR>
<TD height="100%" colspan="4"> </TD>
</TR>
<TR>
<TD colspan="3">
<TABLE WIDTH=768 BORDER=0 CELLPADDING=0 CELLSPACING=0>
<TR>
<TD width="326">
<IMG SRC="images/s7.gif" WIDTH=326 HEIGHT=48 ALT=""></TD>
<TD background="images/bg16.gif" WIDTH=442 HEIGHT=48>
<div style="padding-top:12;color:A8A8A8" class="tah11">
2010 © Copyright iAS. <Br>
All rights Reserved. Read <a href="#" style="color:467B99" class="tah11">Privacy Policy</a>.</div> </TD>
</TR>
</TABLE> </TD>
<TD width="4%" background="images/bg_tile_2.gif"> </TD>
</TR>
</TABLE>
<!-- End ImageReady Slices -->
<map name="Map">
<area shape="rect" coords="39,2,133,27" href="#">
</map>
<map name="Map2">
<area shape="circle" coords="9,12,9" href="#">
</map>
</BODY>
</HTML>
答案 0 :(得分：2)
它闻起来像是线程安全/范围问题。您已使用ResultSet scriptlet声明将DBProcess和<%! %>声明为JSP的实例变量，因此它已在所有HTTP请求之间共享。我不确定DBProcess，但对于ResultSet（以及顺便提到Connection和Statement）这肯定是一个坏主意。如何在代码的残余中使用DBProcess也是非常可怕的，例如DBProcess.statement.executeQuery()。 Statement 真的是公共字段吗？我不知道这个班级的内部是什么样的，但是，这有点像线程安全/范围问题。
此外，这种90年代的HTML风格编写和在JSP中使用scriptlet实际上并不适合“Copyright 2010”应用程序。你在阅读正确的教程/书籍吗？
答案 1 :(得分：1)
除了BalusC指出的那些问题，
基于描述的症状“ 当servlet重定向页面时，jsp可以显示记录，但是当我从任何其他html页面访问此页面时，它无法显示记录 “和代码” if（request.getAttribute（“dbrec”）！= null） “。
我对该问题的主要疑问是使用 request.getAttribute（“dbrec”）
对于那些从其他html页面直接访问，此值可能为null。我怀疑是重定向的情况，可能有一些代码执行request.setAttribute（“dbrec”，....）