Fetching the form values without clicking submit button

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Javascript

Hello friends,I am working on a JSP file in which I have 3 combo boxes named category, sub category & level. As soon as I select some category, I want to display the corresponding sub category & level in the respective combo-box from the datastore. I used this.form.submit() method for the same but it is not working properly. Can someone suggest me some another way of doing it?
This is my code.

<tr>
<td><h2><Font color=#003366>

Category</Font></h2></td>
<%
String category="";
%>

<td> <select name="quizname" onChange="this.form.submit();">
<Option>--Select--</Option>
<%
for(Quiz q : quiz)
{
%>
<Option name="quizname"><%=q.getCategory()%></Option>
<%
}
%>
</select>
</td></tr>
<tr></tr>
<tr>
<td><h2><Font color=#003366>Subcategory</Font></h2></td>
<td><select name="subcategory">
<%
for(Quiz q : quiz)
{

    if(q.getCategory().equals(request.getAttribute("category")))
    {
        %>

<Option name="subcategory"><%=q.getSubCategory()%></Option>
<%
}
}
%>
</select>

</td></tr>
<tr></tr>
 <tr>
<td><h2><Font color=#003366>Level</Font></h2></td>
<td><select name="level">
<%
for(Quiz q : quiz)
{
    //if(category.equals(q.getCategory()))
    //{
    if(q.getCategory().equals(request.getAttribute("category")))
    {
        %>


<Option name="level"><%=q.getLevel()%></Option>



<%
}
}
%>
</table>
</select>

</td></tr>
<p>&nbsp;</p>
<INPUT TYPE=hidden NAME="email" VALUE=<%=user.getEmail() %>>
 <tr><td><input type="submit" value="Start Quiz"/>
</td></tr>

Thanks in advance.