下拉列表中的值是从数据库中得到的，怎样实现取到下拉列表的值并查询数据库
sql语句：String sql="select * from xiaofei where regname like '%"+userid+"%' and xfdate=从下拉列表中取得的值";
select的语句：
<form name="form" method="post">
<div align="center">
<table width="959" height="524" border="0">
<tr>
<td height="37" colspan="6" align="right"><div align="center">请选择
</div>
<label>
<div align="center">
<select name="aaa" id="aaa" onChange="disSel();">
<%
request.setCharacterEncoding("gb2312");
String strError = null;
String userid=(String)session.getAttribute("user");
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection("jdbc:odbc:goodschaginfo");
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
String sql="select distinct xfdate from xiaofei where regname like '%"+userid+"%' order by xfdate
