How do i get the selected index in jsp from a select "in the same page!!!"

Question

i dont if it si possible but i want to get the selected index form a select implmenting javascript jsp an html something like this:
html:select property="slcLocation" onchange="updateList(this.form)">
<% for (int i=0; i< user.getNumLocaliza();i++)
out.println("<option selected>" + user.getLocation(i,1));
%>
</html:select> </div></td>
...

Answer 1

i try it in the same page but it fails, the code is:
<html:select property="slcLocation" onchange="document.location.href='cajaApertura.jsp?slcLocation='+this.options[this.selectedIndex].value">
<%
for (int i=0; i< user.getNumLocaliza();i++)
out.println("<option>" + user.getLocation(i,1));
%>
</html:select>
</div></td>
</tr>
<tr>
<td><div align="left"><font size="1"><strong><font color="#FFFFFF" face="Verdana, Arial, Helvetica, sans-serif">Caja:</font></strong></font></div></td>
<td bgcolor="#C4B4F3"><div align="center">
<html:select property="slcCaja" onchange="document.location.href='cajaApertura.jsp?asdf='+this.options[this.selectedIndex].value">
<%
int caja;
if (request.getParameter("slcLocation")!=null)
//for (int i=0; i< cajaLocation.getNumCajas (request.getParameter("slcLocation"));i++)
for (int i=0; i< 3;i++)
caja = i+1;
out.println("<option> Caja p " + caja + request.getParameter("slcLocation"));
}else
for (int i=0; i< cajaLocation.getNumCajas (user.getLocation(0,1));i++)
caja = i+1;
out.println("<option> Caja " + caja);
%>
</html:select>
is this correct? what is my mistake?
tnks for your help