I am the implementer of NPN in Jetty.
NPN is implemented by modifying the JDK classes for the lack of a TLS Extension API in the JDK. The NPN versions match strictly a JDK version as specified in the documentation.
For JDK 8 we don't plan to support NPN. Instead, we will support ALPN which is the successor to NPN, and backport the ALPN implementation to JDK 7 too.
The implementations for ALPN are already done in a branch, but not integrated yet in the main Jetty build.
You have to be patient for a little while, we need to finalize a bunch of things and integrate ALPN in Jetty master. When that is done we'll blog about.