I'm pretty spoiled when it comes to ergonomics for libraries I choose to use, and java servlet-based libraries don't do it for me these days.

Last I touched java, Jersey was really exciting to me (https://jersey.github.io/) -- netty + good annotations/flask-like syntax + access to the beast that is the JVM is everywhere I want to be. Jersey doens't necessary force you into the servlet pattern IIRC?