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.

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"?