Help with upload file

[roberto]

I have a html form that submit a file using a INPUT TYPE=FILE field (with ENCTYPE = multipart form data)

All works fine. I can read the input stream from request and works with the uploaded file, but if the user "submit a non exists file", in the input stream i receive some data... but what?
How can i know that the file is not correct ?
thankx

[yohann]

so you succed to upload your file, are you using a servlet, if yes, have you code it or have you download it (and where) ?
sorry, it is a lot of question but uploading is not so easy with jsp... (i think)