Can I use SpringMvc and webflux together?

Question

I would like to use 2 approaches(reactive and standard) in one project.

I tried to migrate one REST API endpoint to reactive webflux and test performance before migrate rest of them. But it didn't work. I added router and handler for him, but until I didn't remove spring-boot-starter-web from dependencies and disable @RestController I got http 404 code all the time. Is it possible or not? Or should I migrate all project to reactive approach?

Answer 1

As explained in the Spring Boot reference documentation, Spring Boot will auto-configure a Spring MVC application if both MVC and WebFlux are available. There are several reasons for this:

• Spring MVC can't run on Netty
• both infrastructure will compete for the same job (for example, serving static resources, the mappings, etc)
• mixing both runtime models within the same container is not a good idea and is likely to perform badly or just not work at all

Depending on the goal you're trying to achieve, there might be several ways to work on this.

If you'd like to use WebClient to optimize for multiple, concurrent remote HTTP calls and use Reactor operators, you can keep using Spring MVC annotated controllers and return reactive types as return values (more on this in this Spring Boot talk).

If you'd like to work on pure scalability and latency (so not necessarily raw throughput), then you could start using spring-boot-starter-webflux and work from there. Note that using blocking APIs (like blocking database calls) is forbidden, and wrapping those with Flux or Mono and scheduling that work on separate thread pools will work against you on the performance side.

Finally, if you'd like to use the functional approach provided by Spring WebFlux, then it won't necessarily perform better. It really depends on your use case and how you implement it.