Spring WebFlux is the alternative to Spring MVC module.
Spring WebFlux is used to create fully asynchronous and non-blocking application built on event-loop execution model.
Project Reactor is the implementation of Reactive Streams specification. Reactor provides two types:
Mono: implements Publisher and returns 0 or 1 elements
Flux: implements Publisher and returns N elements.
https://tech.trivago.com/post/2021-03-16-java-reactive-programming-real-world/