Java Ajax request parameters have null value

Question

I'm trying to make a simple ajax request using Java (JSP + Servlet) and Ajax (jQuery). The Ajax request is working as expected, and the servlet code is reached.

The problem is that I can't get the values of the parameters sent by the request. I get null values.

This is the code in the servlet:

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

    response.setContentType("application/json");

    String perfilId = request.getParameter("perfilId"); //Null value
    String perfilNombre = request.getParameter("perfilNombre");  //Null value


    try (PrintWriter out = response.getWriter()) {
        Gson gson = new Gson(); 
        JsonObject obj = new JsonObject();
        obj.addProperty("mensaje", "Algún mensaje. Id: " + perfilId + ", Nombre: " + perfilNombre);

        out.print(gson.toJson(obj));
        out.flush();
    }
}

Ajax request inside a JSP:

$.ajax({
    type: "POST",
    url: 'srvl_def',
    cache: false,
    contentType: "application/json;",
    dataType: "json",
    data: {
        perfilId: $('#perfilId').val(),
        perfilNombre: $('#perfilNombre').val()
    }, 
    success: function (data) {
        alert(data.mensaje);

    }
});

The request data looks like this:

perfilId=1&perfilNombre=nuevo

Perhaps I'm missing something?

EDIT

This is the HTML

    <input type="text" id="perfilId" />
    <input type="text" id="perfilNombre" />

    <button type="button" id="btnGuardar">Enviar</button>

    <script src="js/jquery.js" type="text/javascript"></script>
    <script type="text/javascript">
        $('#btnGuardar').click(function (){
            //ajax call
        });
    </script>

Answer 1

Following this answer, @ShaunakD referenced this in a comment (see question), I was able to obtain the values sent by the ajax call.

The call looks like this:

var perfilId = $('#perfilId').val();
var perfilNombre =  $('#perfilNombre').val();

$.ajax({
    type: "POST",
    url: 'srvl_def',
    cache: false,
    contentType: "application/x-www-form-urlencoded; charset=UTF-8;",
    dataType: "json",
    data: {
        perfilId: perfilId,
        perfilNombre: perfilNombre
    },
    success: function (data) {
        alert(data.mensaje);
    }
});