库可以联上，但取不到数据，不知为什么，请高手帮帮忙

<%@page import="javax.servlet.*"%>   
<%@page import="javax.servlet.http.*"%>
<html>
<head>
<link  href="/jsp-examples/C/chxnet.css" rel="stylesheet" type="text/css">
<title>提交页面</title>
</head>
<body>
<jsp:useBean id="jdbc" scope="application" class="cn.ac.ict.jdbc"/>
<%String ue=request.getParameter("username"); 
  String pd=request.getParameter("password");
  String sql="select * from [USERTEST] where UNAME ='"+ue+"' and UPASS ='"+pd+"'";
  ResultSet rt;
  rt=jdbc.query(sql);
 while(rt.next())
  {session.setAttribute("username",ue);%>
 <iframe><table width="201" height="200" cellspacing="0" cellpadding="0" bgcolor="#3E85DB">
<tr height="54" valign="middle"><td colspan=2 ><img src="/examples/jsp/images/logtu1.gif"></td></tr>
<tr><td><lable>欢迎您：</lable></td><td><%out.print((String)session.getAttribute("username"));}%></td><tr>
<tr><td><input  type="button" value="退出" onclick="1.jsp"></td><td></td></tr><iframe>
</body>
</html>
jsp页面错误提示如下：org.apache.jasper.JasperException: Exception in JSP: /login.jsp:1815:   String sql="select * from [USERTEST] where UNAME ='"+ue+"' and UPASS ='"+pd+"'";
16:   ResultSet rt;
17:   rt=jdbc.query(sql);
18:  while(rt.next())
19:   {session.setAttribute("username",ue);%>
20:  <iframe><table width="201" height="200" cellspacing="0" cellpadding="0" bgcolor="#3E85DB">
21: <tr height="54" valign="middle"><td colspan=2 ><img src="/examples/jsp/images/logtu1.gif"></td></tr>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:467)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:389)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause java.lang.NullPointerException
org.apache.jsp.login_jsp._jspService(login_jsp.java:72)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.23 logs.tomcat提示以下错误：数据库查询失败