Spring Boot 2 reactive webflux

Question

I'm approaching Spring Boot 2 and its reactive way to implement web services. As almost everybody who is used to program with classic synchronous MVC pattern, I have some doubts about this approach. I'm trying to implement a restcontroller and to develop some reactive and non-reactive methods as title of example, in order to understand better the concepts. For instance, importing WebFlux (which uses Netty as Embedded Server) in the way they are written, are the second and the fourth methods reactive, while the first and the third method non-reactive?

@org.springframework.web.bind.annotation.RestController
public class RestController {

  @Autowired
  NoteDao noteDao;

  /* non-reactive */
  @RequestMapping("/hello")
  public String sayHello(){
    return "Hello pal";
  }

  /* reactive */
  @RequestMapping("/hello/reactive")
  public Mono<String> sayHelloReactively(){
    return Mono.just("Hello reactively, pal!");
  }

  /* non-reactive */
  @RequestMapping("/notes")
  public List<Note> getAllNotes(){
    return noteDao.findAll();
  }

  /* reactive */
  @RequestMapping("/notes/reactive")
  public Flux<List<Note>> getAllNotesReactively(){
    return Flux.just(noteDao.findAll());
  }

}

Brian Clozel Brian Clozel · Accepted Answer · 2018-01-16T08:41:06

sayHello and sayHelloReactively can be both considered as reactive - you're basically returning something from memory, no I/O is involved. The second one wraps the String value for no reason - both methods are equivalent.

The core idea behind reactive is that for everything that involves I/O operations (reading and writing from the network, for example), your code should not sit doing nothing while waiting for the result (REST call, database query) to come back. You can think of it as callbacks, plus many additional features like backpressure.

Because NoteDao exposes synchronous+blocking methods, you can't call one method and be notified as soon as the result comes. Wrapping a blocking call with Flux.just will just make things worse. In a WebFlux application, there are very few threads - and doing that will block one for each call - it is then pretty easy to completely crash your application.

If you want to understand more the core ideas behind blocking vs. reactive, you should check out this talk: Servlet or Reactive Stacks: The Choice is Yours. Oh No... The Choice is Mine! - Rossen Stoyanchev.

Spring Boot 2 reactive webflux

1 Answers