sending a selected value from a dropdownlist to a servlet with xhr

Question

I am trying to send the clicked value of a dropdown list to my servlet to run a SQL query using the value received. To do it I am using Ajax like that:

function showProject(prj) {
    xmlhttp = GetXmlHttpObject();
    if (xmlhttp == null) {
        alert ("Browser does not support HTTP Request");
        return;
    }

    var url = "ServletxmlGenerator.java";
    idprj = prj.options[prj.selectedIndex].value;
    url = url + "?idprj=" + idprj;

    xmlhttp.onreadystatechange = stateChanged;
    xmlhttp.open("GET",url,true);
    xmlhttp.send(null);
}

The servlet when

String projectcode=(String) request.getParameter("idprj");

returns null.

When I select a value from the JSP that construct the dropdown list and from which the function showProject is handled the same thing is happned. It returns always null. So the parameter(idprj) is not passed anyway. How can I handle with this. I need to send the selected value to the servlet to run my SQL query.

Answer 1

Just debug your Javascript code. What does for example this say?

idprj = prj.options[prj.selectedIndex].value;
alert(idprj);

For better debugging, I suggest to pick Firebug.

Also debug your Servlet by executing it independently (just enter its URL in browser address bar like http://example.com/contextname/ServletxmlGenerator.java?idprj=1) and by tracking the request and Servelt code.