title: Informing the user that the file is being generated in a download servlet
body: <p>I have a download servlet which generates a ZIP with some files, one of them pretty big, and then sends the generated file in the response for download.</p>
  <p>The problem is that the generating process is pretty big, and between the step of the generation of de ZIP and the download step (when the user see the download dialog) many seconds or even a minute could pass. So I would like to inform the user by anyway that the file is being generated.</p>
  <p>The solution I'm thinking about is doing several requests, one for open a modal window which informs the user and inside this, then do another request automatically to an action which generates the file in a temp location and then, when the request ends, another one which closes the window (the window must be closed automatically) and then request to the download servlet the generated file in the last step.</p>
  <p>If somebody understands what I'm trying to do, I would like if exists a better and cleaner solution.</p>