Chained combobox fails to work

[Rajkumar balakrishnan]

Hi friends,
In my JSP page i want to link one check box with another ie..chained combo box. When i select a option from combo box then the values of the other controls also change.So i decided to write a piece of code that uses JDBC to retrieve data from MySQL and displayed it here. Here is the piece of code that i used to do my job.]

<select name="vendor">
<%  
String cond=null;
dbmodel db=new dbmodel();
ResultSet rs=null;
PreparedStatement ps=null;
db.connect();
String SQL="SELECT * FROM tbl_vendor";
ps=db.con.prepareStatement(SQL);
    rs=ps.executeQuery();
  while (rs.next()){
%>
          <option value="<%=rs.getString("vendor_id")%>"><%=rs.getString("vendor_id")%></option>
          <%}
  String vendname=null;
  String vendaddr=null;
  String vendpass=null;
  out.print(cond);
  String SQL1="SELECT * FROM tbl_vendor WHERE vendor_id="+cond;
  ps=db.con.prepareStatement(SQL1);
  rs=ps.executeQuery();
  while(rs.next())
  {
  vendname=rs.getString("vendor_name");
vendaddr=rs.getString("vendor_address");
vendpass=rs.getString("vendor_password");
  }  
  %>
      </select>                          </td>
                            <td width="86" class="style3">Vendor Name <span class="style4">* </span></td>
                            <td width="158">
                              <input type="text" name="textfield2">                            </td>
                          </tr>
                          <tr>
                            <td class="style1">Vendor Address </td>
                            <td>
                              <textarea name="textarea" cols="18"><%=vendaddr%></textarea>                            </td>
                            <td class="style3">Vendor Address <span class="style4">*</span> </td>
                            <td>
                              <textarea name="textarea2" cols="18"></textarea>                            </td>
                          </tr>
                          <tr>
                            <td class="style1">Vendor Name </td>
                            <td>
                              <input type="text" name="textfield3" value="<%=vendname%>">                            </td>
                            <td class="style3">Vendor ID<span class="style4">*</span></td>
                            <td>
                              <input type="text" name="textfield4">                            </td>
                          </tr>
                          <tr>
                            <td class="style1">Password</td>
                            <td>
                              <input type="text" name="textfield5" value="<%=vendpass%>">                           </td>
                            <td class="style3">Password<span class="style4">*</span></td>
                            <td>

Yes i know this isn't a correct solution and try to do it by some other methods. If you had some idea to put in my post please suggest me one or else tell me whats wrong is in my JSP page...