control the state of download

Hi everybody,

I have a download application in a wapserver, which is a link to a mid file for exemple. I can t do the download with a binary transfert (my boss doesn t want)
But it s would be very great to know if the file has really been downloaded or not... Because today, I just update a download state at the end of the file, but it considers the file downloaded before downloading it.... It means that if there is a problem in the dl, it won t be known.

That s why I thought using a error.jsp?error=404 for exemple to make the state of the download.
But I only know how to do it by a static way ie I can t pass parameters since I declare it in my web.xml.
Do U know how to catch a 404 page dynamically?
Best Regards,
Julien