Comet library for android

Task:开发者_StackOverflow Send messages from server to the android client with response-time minimization.

I've been told that COMET is a good way to perform it. I found this link, but as a client side code only javascript is shown. So, it is neccesary to implement it in java, but I wonder is there any ready comet library for android of for pure java?

Or are there some other good ways to perform messaging?

I want to highlight that server-polling is not acceptable, as it requires much traffic and is very slow.

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How about using cloud to device messaging (C2DM) services to get push notifications when new data is available at the server? Does this yield enough "response time minimization"?