The Undertow 1.2 branch now supports the latest draft of the HTTP2 spec. We have a demo site up and running at https://http2.undertow.io.

So far, we have verified HTTP/2 interop with the following browsers:

The demo site contains instructions for testing it out, including getting it running locally. The HTTP2 code is still quite new, and will be evolving a lot over the coming months. For now most features of HTTP2 are supported, with the exception of priority, which is ignored.