Question

I have a situation that seems to fit the Async Servlet 3.0 / Comet situation but all I need to do is return a 200 response code (or other) after accepting the incoming parameters.

Is there a way for a HttpServlet to complete the http request/response handshake and yet continue processing?

Something like…

doPost( req, response ) {
   // verify input params...
   response.setStatus( SC_OK );
   response.close();
   // execute long query
}     

EDIT: Looking at the javax.servlet package – the proper phrasing to my question is

How do I commit a response?

as in Servlet.isCommitted()

Answer 1

Here’s how I’ve handled this situation:

1. When the app starts up, create an ExecutorService with Executors.newFixedThreadPool(numThreads) (there are other types of executors, but I suggest starting with this one)
2. In doPost(), create an instance of Runnable which will perform the desired processing – your task – and submit it to the ExecutorService like so: executor.execute(task)
3. Finally, you should return the HTTP Status 202 Accepted, and, if possible, a Location header indicating where a client will be able to check up on the status of the processing.

I highly recommend you read Java Concurrency in Practice, it’s a fantastic and very practical book.