Receiving null parameters from request in JSP file when are being sent - ajax

Question

I've a JSP app. It uploads a file, but to do so the user has to authenticate using a name and a password. So my JSP file starts with:
//0.2.- We get the password
String password = (String) request.getParameter("pass"); // -> This returns NULL
//0.3.- We get the "uvus"
String uvus = (String) request.getParameter("uvus"); //-> This also returns NULL
//More code
So I'm trying to know why am I getting null from those variables.
I went to the form I was uploading, and look for the data that was being sent. Using Firefox Debug Tools, I saw:
So in fact, it was being sent.
As additional info, I'm building the request like this:
var pUvus = document.getElementById("uvus").value;
var pPassword = document.getElementById("pass").value;
var file = document.getElementById("userFile");
var formData = new FormData();
formData.append("upload", file.files[0]);
formData.append("uvus", pUvus);
formData.append("pass", pPassword);
xmlhttp.open("POST","uploadFile.jsp",true);
xmlhttp.send(formData);
At last, I would like to say that I can get vars from application object in the same JSP with no errors, and have received in another pair of JSP files vars at request object without more problems, so I think my fault should be in the way I'm building the request in Ajax, but I've no more clue about that...
Anyone can guide me?
Thanks for your help
Update: #rickz asked for how do I get the file and parse the request (what is done after my problem, trying to get the objects from the request scope):
List items;
items = servlet_up.parseRequest(request);
for(int i=0;i<items.size();i++)
{
FileItem item = (FileItem) items.get(i);
if (! item.isFormField())
{

Answer 1

request.getParameter() won't work for a multipart/form-data request.
If you are using org.apache.commons.fileupload then you should be using something like
if(item.isFormField()){
name = item.getFieldName();
...
}