Question

I have a web application in which one of the workflows, users can download files that are dynamically generated. The input is a form which has parameters needed to generate the file.

My current solution is to let them submit this form & on the servlet side I change the response header – content disposition to be an attachment & also provide an appropriate mime-type.

But I find this approach to be inadequate. Because there are chances that the generation of file can take a very long time, in such cases after a certain timeout I directly get 500 or 503 errors in the browser. I guess this is to be expected for the current approach.

I want my workflow to be flexible enough to tell the users as soon as they submit the form that it might take time for the file to generate & that we will display the link to the file as soon as it is ready. I guess I can also email the file or this message to them, but this is not ideal.

Can you guys suggest me an approach for this problem? Should I be more specific in providing information? Any help appreciated.

Answer 1

If you want to do this synchronously (i.e. make the user wait for the document to be ready rather than have them go off and do other things while waiting) a traditional approach is to bring them to a “report loading” page.

This would be a page that:

• 1) informs them that the report is loading.
• 2) refreshes itself (either using the meta refresh tag or javascript)
• 3) upon refresh, checks to see if the report is ready and either:
  • a) goes back to step 1 if it isn’t ready
  • b) gives them the document if it is ready.

Synchronous is kind of old-school, but your question sounded like that was the approach you wanted.

Asynchronous approaches would include:

• Use Ajax to make a link to the document appear on the page once it is ready.
• Have a separate page that shows previously generated documents. The use can go to this page at their leisure, and, meanwhile, they can browse the rest of the site. This requires keeping a history of generated documents.
• As you suggested, send it via e-mail.