Spring MVC (async) vs Spring WebFlux

Question

I\'m trying to understand Spring WebFlux. The things I\'ve found so far are reactive at the core, no Servlet API, no thread per request, HTTP 2, server pushes, application/strea

Answer 1

The Servlet async model introduces an async boundary between the container threads (1 Servlet request/thread model) and the processing of the request in your application. Processing can happen on a different thread or wait. In the end, you have to dispatch back to a container thread and read/write in a blocking way (InputStream and OutputStream are inherently blocking APIs).

With that model, you need many threads to achieve concurrency (because many of those can be blocked waiting for I/O). This costs resources and it can be a tradeoff, depending on your use case.

With non-blocking code, you only need a few threads to process a lot of requests concurrently. This is a different concurrency model; like any model, there are benefits and tradeoffs coming with it.

For more information about that comparison, this Servlet vs. Reactive stacks talk should be of interest.