And at work, we're now rewriting all those NodeJS services in Go or Java.

We hired some Node maintainer(s) a long time ago, rumor has it, who got us on the Node train.

How do you do async in java? While it does have CompletableFutures now, none of the libraries (specifically databard drivers) seem to support it, so I always end up with a blocked thread per request.

Java has had non-blocking IO for some time. https://en.wikipedia.org/wiki/Non-blocking_I/O_(Java)

Unfortunately it seems difficult to use (to me at least), but frameworks like netty are build on top of it to provide incredible performance.

However, the fact that Java provides real threading means that a blocking io is not a performance problem if you use the correct patterns.