Java EE (Java Enterprise Edition) General Discussion

I use Apache Commons Fileupload to upload files to my Tomcat server. I am now writing a new application that will allow users to upload (potentially) large files. What I want to do is initiate a progress bar. My plans were to use Ajax and IFrames to upload the file data to my servlet.

But I need to write another servlet (I guess) that can return how many bytes have been uploaded so far, so I can use the data to update a progress bar on the client.

That is my question, how can servlet B check how much of the file servlet A has uploaded?

Any help would be appreciated.