yep @Ted, Spring is a very large framework in the Java world. It started as a small Inversion of Control (IoC) framework way back and has grown into a mammoth framework with lots of features for all types of applications.
The WebFlux feature is based on Project Reactor. It is basically a non-blocking solution and control of back pressure.
I’m still learning it and was wondering if anyone else was using it.
Just now I have found a tutorial on GitHub that I did not know exists, so for anyone interested this might be helpful:

Head First Reactive with Spring

I wondered what WebFlux was and found this - posting here in case anyone else is curious

The original web framework included in the Spring Framework, Spring Web MVC, was purpose-built for the Servlet API and Servlet containers. The reactive-stack web framework, Spring WebFlux, was added later in version 5.0. It is fully non-blocking, supports Reactive Streams back pressure, and runs on such servers as Netty, Undertow, and Servlet 3.1+ containers.

Both web frameworks mirror the names of their source modules (spring-webmvc and spring-webflux) and co-exist side by side in the Spring Framework. Each module is optional. Applications can use one or the other module or, in some cases, both — for example, Spring MVC controllers with the reactive WebClient.

I think @Ted has some experience with Spring tho not sure if he’s used WebFlux - hopefully he’ll spot this and be able to confirm

Sorry, I’ve not used Spring so I’m unable to chime in .

I just know it’s extremely popular in the Java ecosystem.