Event driven with Java and Javascript?

Question

I am trying to perform some computations on a server. For this, the client initially inputs some data which I am capturing through Javascript. Now, I would perhaps make a XMLHttpRequest to a server to send this data. Let's say the computation takes an hour and the client leaves the system or switches off the system.

In practice, I would use perhaps polling from the client side to determine if the result is available. But is there some way I could implement this in the form of a call back, for instance, the next time the client logs in, I would just contact the client side Javascript to pass the result... Any suggestions? I am thinking all this requires some kind of a webserver sitting on the client side but I was wondering if there's a better approach to do this.

Answer 1

Your best bet is to just poll when the user gets to the web page.

What I did in something similar was to gradually change my polling time, so I would start with several seconds, then gradually increase the interval. In your case, just poll after 15 minutes, then increase every 5 minutes when it fails, and if the user closes the browser then you can just start the polling again.

If you want some callback, you could just send an email when it is finished, to let the user know.

Also, while you are doing the processing, try to give some feedback as to how far you have gone, how much longer it may be, anything to show that progress is being made, that the browser isn't locked up. If nothing else, show a time with how long the processing has been going on, to give the user some sense of progress.