Important to know is that there are two ways to use Spring Webflux. One using annotations, which is quite similar to Spring MVC, and one using a functional way.
Spring MVC is used for synchronous processing, while Spring Webflux for asynchronous processing.
参考
Spring Webflux: Getting started
使用 Reactor 进行反应式编程
聊聊reactive streams的Mono及Flux