This part of the documentation covers support for reactive-stack web applications built on a Reactive Streams API to run on non-blocking servers, such as Netty, Undertow, and Servlet 3.1+ containers.

1. Spring WebFlux

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.

2. WebClient

Spring WebFlux includes a client to perform HTTP requests with. WebClient has a functional, fluent API based on Reactor, see Reactive Libraries, which enables declarative composition of asynchronous logic without the need to deal with threads or concurrency. It is fully non-blocking, it supports streaming, and relies on the same codecs that are also used to encode and decode request and response content on the server side.

3. WebSockets

This part of the reference documentation covers support for reactive-stack WebSocket messaging.

4. Testing

The spring-test module provides mock implementations of ServerHttpRequest, ServerHttpResponse, and ServerWebExchange.

5. RSocket

RSocket is an application protocol for multiplexed, duplex communication over TCP, WebSocket, and other byte stream transports.

6. Reactive Libraries

spring-webflux depends on reactor-core and uses it internally to compose asynchronous logic and to provide Reactive Streams support. Generally, WebFlux APIs return Flux or Mono and leniently accept any Reactive Streams Publisher implementation as input.