Best - and currently active - networking lib?

Hi guys.

I’m about to extend my small engine with networking. It will be used in a FPS game, so I’ve chosen UDP over IP.
Before I jumped in, I’ve done some research and found that the common recommended lib for that is Kryonet, which is not active for a year now, so I think I’ll skip it.

Is there an existing - and active - lib that is commonly used or I have to implement my own? My main goal is not to create a game - it’s only a side goal -, but learn more about game developing and Java. My bets are either or MQTT with for eg. Paho client.

Any suggestions? - either a lib or anything.

Thank you!