What is the closest Java alternative to Twisted?
Like Stephane, I would suggest you take a look at Mina. Its a framework for asynchronous network IO. It is built on top of NIO, which was mentioned earlier, and IMO hides away some of the complexity involved with Selectors,Channels,etc.. I've used Mina for a couple of projects and its pretty good, but be warned, I've found the documentation to be a little weak. And again, like Stephane mentioned, it doesn't have out of the box support for too many protocols.