I don’t recall which Java environment was used; I’m not a Java developer so some of those technical details went in one ear and right out the other. They did implement snapstart for Java lambdas and that made the warm start time similar to Go. But the runtime performance isn’t even close after they put a bunch of effort into trying to optimize it.

I truly can’t recommend anything other than Go for lambdas. It’s better by every metric and it’s a lot easier to manage your infrastructure (just a single binary file with no file or environmental dependencies; it doesn’t get any more straightforward than that.) I’d definitely recommend doing a PoC to compare performance for your specific workload in Java vs. Go. As long as you have devs capable of writing Go, it’s a real winner. If you don’t, I’d still go with nodejs lambdas over Java; Java still seems to require a lot of tweaking to get its performance comparable. It’s a 30 year old swiss army knife, and it shows.