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javaajaxreal-timedashboard

Implementing a realtime, web dashboard

I'd like to implement a dashboard that is web-based and has a variety of metrics where one changes every minute and others change like twice a day. Via AJAX the metrics should be updated as quick as possible if a change occured. This means the same page would be running for at least several hours.

What would be the most efficient way (technology-/implementation-wise) of dealing with this in the Java world?

Solution

  • Well, there are two obvious options here:

    • Comet, aka long polling: the AJAX request is held open by the server until it times out after a few minutes or until a change occurs, whichever happens first. The downside of this is that handling many connections can be tricky; aside from anything else, you won't want the typical "one thread per request, handling it synchronously" model which is common.
    • Frequent polling from the AJAX page, where each request returns quickly. This would probably be simpler to implement, but is less efficient in network terms (far more requests) and will be less immediate; you could send a request every 5 seconds for example, but if you have a lot of users you're going to end up with a lot of traffic.

    The best solution will depend on how many users you've got. If there are only going to be a few clients, you may well want to go for the "poll every 5 seconds" approach - or even possibly long polling with a thread per request (although that will probably be slightly harder to implement). If you've got a lot of clients I'd definitely go with long polling, but you'll need to look at how to detach the thread from the connection in your particular server environment.