非常棘手得一个问题!!! 大家帮帮忙~谢拉

源码:
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<jsp:useBean id="DBManager" class="DBConnection.DBConnManager" scope="application" /><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>酒店客房管理系统</title>
<link rel="stylesheet" href="images/css.css" type="text/css" media="screen">
</head><body leftMargin="0" topMargin="0" marginheight="0"  marginwidth="0" >
  
<%
 
  Connection con= DBManager.getConnection("mysql");
    if(con==null)
{
%>
   <p><font color="red">数据库正忙！！！</font></p>
<%
    }
Statement stmt=con.createStatement();%><form name="form1" method="post" action="">
  <table width="844" border="1" height="25">
    <tr>
      <td width="9%" background="images/bt1.jpg"> <div align="center">客房类型编号 </div></td>
      <td width="9%" background="images/bt1.jpg"><div align="center">客房名称</div></td>
      <td width="9%" background="images/bt1.jpg"> <div align="center">客房面积 </div></td>
      <td width="9%" background="images/bt1.jpg"> <div align="center">配置床位 </div></td>
      <td width="9%" background="images/bt1.jpg"> <div align="center">客房价格 </div></td>
      <td width="20%" background="images/bt1.jpg"> <div align="center">配置空调 </div></td>
      <td width="20%" background="images/bt1.jpg"> <div align="center">配置电视 </div></td>
  <td width="15%" background="images/bt1.jpg"> <div align="center">操作</div></td>
    </tr>
 <%
    ResultSet rs=stmt.executeQuery("select * from roomcategory");
while(rs.next())
{
 %>
    <tr>
    <td><div align="center"><%= rs.getString("RCategoryId") %></div></td>
<td><div align="center"><%= rs.getString("Name") %></div></td>
<td><div align="center"><%= rs.getString("Area")%></div></td>
<td><div align="center"><%= rs.getString("BedNum")%></div></td>
<td><div align="center"><%= rs.getString("Price")%></div></td>
<td><div align="center"><%= rs.getString("AirCondition")%></div></td>
<td><div align="center"><%= rs.getString("TV")%></div></td>
<td><div align="center"><a href="room_modify_1.jsp" target=adminmain>修改</a></div></td> 
</tr>        
<%
}
con.close();
stmt.close();
DBManager.releaseConnection("mysql",con);
 %>
  </table>
</form></body>
</html>
    错误代码:
root cause javax.servlet.ServletException
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:858)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:791)
org.apache.jsp.room_005flist_jsp._jspService(room_005flist_jsp.java:140)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:332)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.StackOverflowError
java.util.Vector.indexOf(Unknown Source)
java.util.Vector.removeElement(Unknown Source)
DBConnection.DBConnPool.getConnection(DBConnPool.java:35)
DBConnection.DBConnPool.getConnection(DBConnPool.java:40)
DBConnection.DBConnPool.getConnection(DBConnPool.java:40)
DBConnection.DBConnPool.getConnection(DBConnPool.java:40)
DBConnection.DBConnPool.getConnection(DBConnPool.java:40)