Spring 5 has a reactive stack baked into it, using which, web applications can be built on top of Reactive Streams capable of running on new non-blocking servers, such as Netty, Undertow, and Servlet containers, running on Servlet specifications greater than 3.1.

Existing web application frameworks, such as Spring MVC, are built for Servlet containers from the outset, but Spring 5 brings with it a new web application framework, Spring WebFlux, created with reactive in mind. We have a dedicated chapter in this book covering Spring WebFlux (Chapter 5, Integrating with Spring WebFlux), so I won't be delving deep into this here. It's good to know that Spring 5 has serious thoughts on reactive and that it is reflected clearly in all these new additions.

Spring WebFlux requires Reactor to be included as one of its core dependencies. But, as always, it does allow you to switch implementations quite easily, if needs be.