String name = request.getParameter("type");
String queryString = "SELECT * FROM Customer WHERE TYPE='Provider';";
rs = statement.executeQuery(queryString);
while(rs.next()) out.print(rs.getString(2));
什么都不打印，为什么？我检查了数据库连接，但我已成功连接到它。可能是什么问题？
jsp中的整个代码。我认为整个代码存在问题。这有什么问题？
<%@page import="java.sql.Statement"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.Connection"%>
<head>
<meta charset="utf-8">
<title>GET CUSTOMER LIST</title><meta name="keywords" content="contact, direction,"><meta name="description" content="">
<meta name="HandheldFriendly" content="True">
<meta name="MobileOptimized" content="320">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
<meta name="format-detection" content="telephone=no">
<meta name="format-detection" content="address=no">
<link rel="canonical" href="#">
<link rel="apple-touch-icon-precomposed" sizes="114x114" href="http://www.onbile.com/nbproject/private/sushi/media/icon/apple-touch-icon.png">
<link rel="apple-touch-icon-precomposed" sizes="72x72" href="http://www.onbile.com/nbproject/private/sushi/media/icon/apple-touch-icon.png">
<link rel="apple-touch-icon-precomposed" href="http://www.onbile.com/nbproject/private/sushi/media/icon/apple-touch-icon-precomposed.png">
<link rel="shortcut icon" href="http://www.onbile.com/nbproject/private/sushi/media/icon/apple-touch-icon.png">
<!-- Mobile IE ows us to activate ClearType technology for smoothing fonts for easy reading -->
<meta http-equiv="cleartype" content="on">
<link rel="shortcut icon" href="http://www.onbile.com/favicon.ico">
<style type="text/css" media="screen">
/*reset*/
html, body { margin: 0; padding: 0; border: 0; }
body { font-family:Helvetica, Arial, sans-serif; line-height:1.5; font-size:16px; background: #fff; color: #333; word-wrap: break-word; -webkit-text-size-adjust: none; }
h1, h2, h3, h4, h5, h6{ font-weight: normal; margin: 0;}
p img { float: left; margin: 0 10px 5px 0; padding: 0; }
img { border: 0; max-width: 100%; }
table { width:auto; border-collapse: collapse;border-spacing: 0; }
article, aside, details, figcaption, figure, footer, header, hgroup, nav, section { display: block; }
/*Non-semantic helper classes*/
.ir { display: block; border: 0; text-indent: -999em; overflow: hidden; background-color: transparent; background-repeat: no-repeat; text-align: left; direction: ltr; }
.ir br { display: none; }
@font-face {
font-family: 'FagoCoRegular';
src: url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-webfont.eot');
src: url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-webfont.eot?#iefix') format('embedded-opentype'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-webfont.woff') format('woff'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-webfont.ttf') format('truetype'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-webfont.svg#') format('svg');
font-weight: normal;
font-style: normal;
}
@font-face {
font-family: 'FagoCoBlackRegular';
src: url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-black-webfont.eot');
src: url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-black-webfont.eot?#iefix') format('embedded-opentype'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-black-webfont.woff') format('woff'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-black-webfont.ttf') format('truetype'),
url('http://www.onbile.com/nbproject/private/sushi/media/font/fagoco-black-webfont.svg#FagoCoBlackRegular') format('svg');
font-weight: normal;
font-style: normal;
}
body {
font-family: 'FagoCoRegular';
}
h2.title1 {
padding: 22px 15px 20px 15px;
line-height: 0.9em;
}
.title2 {
line-height: 0.9em;
}
.title4 {
letter-spacing: -0.05em;
line-height: 1.2em;
}
img.image {
padding: 1px 0;
display: block;
width: 100%;
}
.imgcontent {
position: relative;
overflow: hidden;
border-top-width: 1px;
border-top-style: solid;
border-bottom-width: 1px;
border-bottom-style: solid;
}
img.image.left {
float: left;
}
img.image.right {
float: right;
}
img.image.center {
margin: 0 auto;
}
.order {
margin-bottom: 1px;
border-bottom-style: solid;
border-bottom-width: 1px;
display: block;
padding: 4px;
}
</style>
<link rel="stylesheet" href="http://www.onbile.com/assets/websites/final/052/333/052333/css/52333_f.css"><link rel="stylesheet" href="http://www.onbile.com/assets/websites/final/052/333/052333/css/52333_c.css">
<!--[if gte IE 8.0]>
<style type="text/css">
.t-sushi-p-gallery-content .list-items li {
width: 46%;
}
</style>
<![endif]-->
<script src="http://www.onbile.com/nbproject/private/sushi//js/modernizr.custom.09105.js"></script>
</head>
<body>
<div id="container">
<header class="t-sushi-p-header int">
<div class="header">
<span class="adorn"></span>
<a href="http://tekirmobile.onbile.com/" class="btn back ir">back</a>
<h1 class=""><a href="http://tekirmobile.onbile.com/" id="logotype"><img src="http://www.onbile.com/assets/websites/final/052/333/052333/smooth_logo.png" class=" center" style="width:60%;"></a></h1> <a href="#" class="btn menu ir">menu</a>
<a href="#container" class="btn menu ir on">menu</a>
</div>
</header>
<header class="t-sushi-p-subtitle">
<p title="My own profile" class="subtitle edit_element" id="1688529_subtitle" type="text">My own profile</p>
</header>
<style>
#container:target nav.t-sushi-p-menu.acor ul {
height: 160px;
}
</style>
<nav class="t-sushi-p-menu acor">
<ul>
<li class="selected"><a href="http://127.0.0.1/getCustomerList.html" class="menu">GET CUSTOMER LIST</a></li><li class=""><a href="http://tekirmobile.onbile.com//about-me" class="menu">MONITOR CASH FLOW</a></li><li class=""><a href="http://tekirmobile.onbile.com//curriculum-vitae" class="menu">GET CUSTOMER STATE INFO</a></li><li class=""><a href="http://tekirmobile.onbile.com//photo-gallery" class="menu">MONITOR FINANCIAL TRANSACTIONS</a></li><li class=""><a href="http://tekirmobile.onbile.com//blog" class="menu">GET PAYMENT PLAN</a></li> </ul>
</nav>
<div class="t-sushi-p-contact-content">
<!-- <h2 title="Contact with Mike Stain" class="title1 edit_element" id='1688531_titles' type='text'>Contact with Mike Stain</h2> -->
<h2 class="title1">GET CUSTOMER LIST</h2>
<form name="input" action="/TekirMobile/getCustomerList" method="post">
<table>
<div class="prop">
<span class="value "><select name="type" class="middle" size="1"> <option value="All">All</option>
<option value="Customer" selected="selected">Customer</option>
<option value="Provider">Provider</option>
<option value="Bank">Bank</option>
<option value="Foundation">Foundation</option>
<option value="Agent">Agent</option>
<option value="Branch">Branch</option>
<option value="Contact">Contact</option>
<option value="Related">Related</option>
<option value="Personnel">Personnel</option>
</select>
</span>
</div>
</table>
<br />
<input type="submit" value="Search" name="submit">
<%
try {
/* Create string of connection url within specified format with machine name,
port number and database name. Here machine name id localhost and
database name is usermaster. */
String connectionURL = "jdbc:mysql://localhost:3306/TekirMobile";
// declare a connection by using Connection interface
Connection connection = null;
// Load JBBC driver "com.mysql.jdbc.Driver"
Class.forName("com.mysql.jdbc.Driver").newInstance();
/* Create a connection by using getConnection() method that takes parameters of
string type connection url, user name and password to connect to database. */
connection = DriverManager.getConnection(connectionURL, "root", "fenderpass");
ResultSet rs = null;
Statement statement = null;
if(request.getParameter("submit")!=null)
{
String name = request.getParameter("type");
String queryString = "SELECT * FROM Customer WHERE TYPE='Provider'";
out.print(queryString);
rs = statement.executeQuery(queryString);
for (int i = 1; rs.next(); i++) {
out.println("row=" + i + ": " + rs.getString(2));
}
}
// check weather connection is established or not by isClosed() method
if(!connection.isClosed())
%>
<font size="+3" color="green"></b>
<%
connection.close();
}
catch(Exception ex){
%>
</font>
<font size="+3" color="red"></b>
<%
}
%>
</form>
</div>
</div>
<footer class="t-sushi-p-footer">
<h5 title="" class="title5 edit_element" id="1688532_title_contact" type="text"></h5>
<div class="small edit_element" id="1688532_contact_description" type="textarea"><p>©2012 | License | Privacy | Özgür Yaz?l?m </p></div>
</footer>
<div class="t-sushi-p-social">
<ul class="social">
<li class="facebook" id="facebook_elem">
<a href="http://www.facebook.com/" class="" target="_blank">Facebook</a>
</li><li class="twitter" id="twitter_elem">
<a href="http://www.twitter.com/" class="" target="_blank">Twitter</a>
</li><li class="linkedin" style="display:none" id="linkedin_elem">
<a href="http://www.linkedin.com/" class="" target="_blank">Your Linkedin</a>
</li><li class="skype" style="display:none" id="skype_elem">
<a href="http://www.skype.com/" class="" target="_blank">Your Skype</a>
</li><li class="flickr" style="display:none" id="flickr_elem">
<a href="http://www.flickr.com/" class="" target="_blank">Your Flickr</a>
</li><li class="youtube" style="display:none" id="youtube_elem">
<a href="http://www.youtube.com/" class="" target="_blank">Your Youtube</a>
</li><li class="google" style="display:none" id="google_elem">
<a href="http://www.google.com/" class="" target="_blank">Your Google</a>
</li><li class="email" style="display:none" id="email_elem">
<a href="mailto:" class="" target="_blank"></a>
</li>
</ul>
</div>
</div> <!--! end of #container -->
<div style="height:51px;width:100%;clear:both"> <br></div>
<div style="position:fixed; bottom:0px;margin-left:auto;margin-right:auto">
<!--qzkqc-->
</div>
</div>
</body>
答案 0 :(得分：5)
很可能是因为没有返回结果。
答案 1 :(得分：1)
我会尝试一些事情：
在查询结尾处删除分号。传入语句的SQL查询不需要以分号结尾。
将显示的最后一行更改为
for (int i = 1; rs.next(); i++) {
out.println("row=" + i + ": " + rs.getString(2));
}
这样你可以判断根本没有返回任何行，或者返回的所有行都是空字符串。
您的语句永远不会被初始化，尝试使用它将导致NullPointerException。您可能会抛出一个您未看到的异常，因为它会在catch块中没有跟踪的情况下被吃掉。编辑catch块以显示异常中的堆栈跟踪，如下所示：
}
catch(Exception ex){
ex.printStackTrace();
}