Question

I have a long-running task (report) which would exceed any TCP connection timeouts before it starts returning data. Asynchronous servlets (introducted in Servlets 3.0) are exactly what I need, however I am limited to Servlet v2.4.
Are there any “roll-your-own” solutions? What I’m doing feels hacked – I kick off the task asynchronously in a thread and just return to the client immediately. The client then polls every few seconds (with ajax), and checks for a “ready” status for this task ID (a static list maintains their status and some handles to the objects processed by the thread). Once ready, I inject the output stream into the work object so the thread can write the results back to the client.

Answer 1

You can implement the Reverse ajax technique which means that instead of polling many times to get the response you get the response once the task has finished.
There is a quick solution to implement reverse-ajax technique by using DWR here. But you should maintain the use of the static List. If your background task business logic is complicated you can use an ESB or something more sophisticated.