Http4s VS Vert.x

http4s is a Typelevel project, and therefore falls into the "program in Scala as if it were Haskell" category. Many people find this off-putting, but honestly, I think with the resources listed above, this is the option at the best intersection of "mature" and "well-documented" available in Scala. The reason it's off-putting to many people is that Haskell-style pure FP isn't mainstream, so it isn't so much a matter of learning a new technology as it is a matter of learning a new paradigm, which necessarily means surfacing and unlearning things you already know, and perhaps confronting the uncomfortable feeling that things you thought were "fundamental," "have to be that way," aren't, and don't. I personally found this process liberating. But not everyone does.

If you want a mature REST API library, I recommend http4s. Be aware, though, that it’s based on purely-functional programming with Cats, cats-effect, and fs2, so if you’re not familiar with them or aren’t prepared to commit to the paradigm, the learning curve may be daunting, seem pointless, or both.

See also cats-effect and fs2. cats-effect gives you your IO Monad (and IOApp to run it with on supported platforms). fs2 is the ecosystem’s streaming library, which is much more pervasive in functional Scala than in Haskell. For example, http4s and Doobie are both based on fs2.

Most important/known: * https://http4s.org/ - an HTTP client/server * https://github.com/typelevel/fs2 - streaming * https://github.com/tpolecat/doobie - JDBC

Scala devs are too busy wondering about free monads and F[Request[F] => Response[F]]. I am very pleased by http4s, Doobie, ScalaJS, and the whole ecosystem, really: https://http4s.org

In reality, your performance issues will not be http4s, but something else. That being said, there are improvements that http4s can and is making, and I'm quite excited about the future 1.0 release, which has some important and fundamental performance improvements already, like a a 125% performance improvement on the plaintext benchmark from https://github.com/http4s/http4s/pull/6091 - and finally, yes, akka-http does have very good performance, but you can also get good performance out of http4s.

http4s for REST services.

This is a long list of misunderstandings I don’t have the patience to unpack. Instead, let me refer you to the links in my top comment in the thread, then suggest you learn at least http4s, a purely-functional web service library that’s been used in production for a decade or so now.

I would say http4s and Doobie. Both are pure FP libraries in the Typelevel ecosystem. Both are exceptionally clear, extremely reliable, extremely pleasant to use… I like to point out http4s, in particular, is primarily a collection of types modeling the relevant RFCs. What behavior it has comes overwhelmingly from the underlying Cats, cats-effect, and fs2 libraries. This reflects the generality of those underlying libraries and the intense focus of the http4s team. The same applies to Rob Norris and Doobie, which tames JDBC as well as it can be tamed, IMO.

The most popular nowadays are - I guess - akka-http and http4s. You can also use Play if you don't want to start from scratch but prefer a framework-based approach.

Hibernate Reactive integrates with Vert.x, but an extension allows to bridge to Project Reactor if wanted

Explicitly so:

Personally, I like vertx, it is modular and you can pick and choose what you need. It also has support for kotlin coroutines, https://vertx.io/, https://github.com/vert-x3/vertx-examples/tree/4.x/kotlin-examples

I really like Eclipse Vert.x... As both an Erlang dev and Java dev, it's a great synergy and soon to have support for Virtual Threads similar to BEAM.

There are many lean, popular, non-magical libraries in Java land. (https://quarkus.io/, https://vertx.io/, etc). Spring is a monster 😱. Its like comparing Kubernetes (written in Go) with some lean framework in another lang.

Eclipse Vert.x - Add amazing Async to any Java stack

Vert.X example: https://github.com/eclipse-vertx/vert.x/blob/master/src/main/java/examples/EventBusExamples.java#L106 (couldn't even find docs)

In fact, it builds on top of proven standards such as Eclipse MicroProfile or frameworks such as Vert.x or JAX‑RS.

If you’ve used NodeJS & ExpessJS, in Java world, Vert.x, Helidon and Javalin should be familiar.