How to Return Flux as response when using Spring Reactor and Spring Boot?

Question

I am trying to use Spring Reactor with my Spring Boot application.

I am using Project Reactor 3.0.7.RELEASE and Spring Boot 1.5.3.RELEASE.

I have a method in my Service class which returns Flux.

I want to return the value to controller in web layer. But, I do not see the values returns in the json response.

When I invoke http://localhost:8080 from browser, I get response as, {"prefetch":-1}

I am not sure if I should I do some conversion from Flux to String before returning the response.

I have my code shared in , https://github.com/bsridhar123/spring-reactor-demo/blob/master/src/main/java/com/demo/reactor/ReactiveApp.java

Can you please help me on the correct approach for it.

Answer 1

Full reactive support using Reactor is only implemented in Spring 5 (currently in RC phase) and Spring Boot 2 (currently in Milestone phase).

You can use Reactor independently of Spring, but that doesn't make the framework reactive and asynchronous so you lose some benefit. You cannot simply return a Flux as the framework doesn't yet understand this type.

However, I believe it can still be useful in the service layer, if you have to orchestrate a lot of service calls.

What you can do in this case is to use Flux and Mono throughout your service layer and convert those to Spring 4's DeferredResult. Something like:

DeferredResult<ResponseEntity<String>> result = new DeferredResult<>();
service.getSomeStringMono()
       .map(n -> ResponseEntity.ok(n))
       .defaultIfEmpty(ResponseEntity.notFound().build()
       .subscribe(re -> result.setResult(re),
                  error -> result.setErrorResult(error));
return result;