HTTP/2 is still very much new to Java, and as such, there are just two libraries who support it – Jetty (from 9.3), and Netty (in alpha). If you’re going the Jetty way (as I have), you’ll need to add their ALPN library to your boot classpath.
Note: Jetty 9.3.x requires the use of Java 8.
A full library for this is available here, on GitHub.
Here’s a quick example: