They do but the Java ecosystem takes a hit here, with many libraries being slow to initialize. The slower it takes to startup, the longer it takes to absorb the new load, to the point where you either keep some headroom (IOW, waste $$$), or try to predict load (complex, also wastes $$$).
There are attempts to fix this with e.g. Graal, which effectively does the expensive initialization and reflection at compile time, but there are so many downsides and pitfalls right now with Graal that I don't consider it a serious solution to the problem. It's basically creating a new ecosystem, which means one primary motivation--to take advantage of the Java ecosystem--is much less compelling.
This isn't constrained to the public ecosystem, lots of companies have their own internal libraries, and Java makes it very easy and even encourages doing lots of expensive things at startup, like classpath scanning and pre-caching things. For a long time, Java made explicit decisions to de-prioritize startup time to improve maintainability (reflection/scanning/dynamic classloading) and runtime performance (e.g JIT). This tradeoff doesn't work out so well in a world of ephemeral processes that come and go as demand changes.
I guess what's specific to JS, Go, Python, et al is the cultural emphasis on fast startup. Interestingly these all come from different constraints but the net result is that, in general, you can go from cold to serving traffic much faster than with Java, with a lot less effort.
> There are attempts to fix this with e.g. Graal, which effectively does the expensive initialization and reflection at compile time, but there are so many downsides and pitfalls right now with Graal that I don't consider it a serious solution to the problem. It's basically creating a new ecosystem, which means one primary motivation--to take advantage of the Java ecosystem--is much less compelling.
I'm not sure I understand what the downsides are for Graal and FAAS. There are some pitfalls around reflection but even those don't seem to hard to avoid. Is that what you are referring to?
Graal has incomplete support for Java. Last time I tried a few months ago, ObjectOutputStream was not supported (I think it is now?), which was a critical part of a library I was using, forcing me to abandon Graal.
Dealing with reflection is pretty awful, you have to comb through your entire dependency graph.
Targeting the compiler for a different OS/architecture than the host is difficult, to say the least.
There are so many great languages and runtimes to pick from these days...I can't imagine why anyone would willingly choose a technology like that.
(Don't get me wrong, Graal is a fascinating technology, and I hope that one day it is able to seamlessly compile Java code to native executables...but it's not there yet.)
Not gp but avoiding the reflection pitfalls is not so straightforward at all, you have to chase what your dependencies are doing to satisfy the "closed world" hypothesis. I still like java more than javascript, but writing performant serverless functions using js is way more easy right now
