Strange problem

From:

"Manoj Jain" <Manoj.S.J@gmail.com>

Newsgroups:

comp.lang.java.help

Date:

3 Jun 2006 06:17:25 -0700

Message-ID:

<1149340645.049900.141820@f6g2000cwb.googlegroups.com>

hello
I'm developing a small code to display models and submodels for cars.

when one clicks on a submenu, it calls SubModelServlet, where I
populate models from database into a vector object, put into request
object and dispatches to ModelView.jsp page.
where I display list of models into drop down box.<select></tag>

In short, problem is every time i visit the page, it doubles the
content items in drop down box.
code for above
//When one clicks on SubMenu it navigates to SubMenuServlet where foll.
is done.
            stmt=conn.createStatement();
            String query="select * from \"ModelMaster\"";
            res=stmt.executeQuery(query);
            while(res.next())
            {
                ConcreteModelDTO modelDTO=new ConcreteModelDTO();
                modelDTO.setMIndex(res.getInt("MIndex"));
                modelDTO.setModel(res.getString("model"));
                vModel.addElement(modelDTO);
            }

            res.close();
            stmt.close();
            request.setAttribute("models",vModel);

rd=getServletContext().getRequestDispatcher("/SubModelView.jsp");
            rd.forward(request,response);

SubModelView.jsp
<%
   StringBuffer modelOption=new StringBuffer();
                       Vector
vModel=(Vector)request.getAttribute("models");
                       Iterator it=vModel.iterator();
                       while(it.hasNext())
                       {
                           ConcreteModelDTO
modelDTO=(ConcreteModelDTO)it.next();
                           modelOption.append("<option
value=\""+modelDTO.getMIndex()+"\">"+modelDTO.getModel()+"</option>");
                       }
                    %>

<html>
    <head >
        <meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
        <title>Model</title>

</head>
    <body>

            <td><h4>Model Type</h4></td>
            <td>
<%= "<select name=\"cmbModel\" id=\"cmbModel\">"+modelOption
+"</select>"%>
</td>
<td><h4>Sub Model Type</h4></td>
            <td><input type=text id="txtSubModel"></td>
        <tr>
            <td><INPUT type=button value="Create SubModel"
name="btnCreate" class='btn' onclick="selectModel(this)"></td>
        </tr>
    </table>

</table>

Every time i calls jsp page, either by through clicking on menu or
refreshing, it shows the page but with doubled drop down contents.

please help me out.