Hello, with my team we want to make a progressive ...

# spring

[pdegand]

Hello, with my team we want to make a progressive transition to webflux.
But we would like to use the coroutine support of webflux instead of Mono/Flux.
I’ve seen in the presentation from Sébastien at KotlinConf that the support for coroutine in WebMVC controllers are not available yet.
I’m wondering if it’s a good alternative to begin refactoring the app to have a big runBlocking { } inside the WebMVC controller until all of the controller are refactored, and when we are ready, to remove the dependency to webmvc to enable the full reactive stack, remove all the runBlocking and convert the controller methods to suspend ?

[sdeleuze]

Since Deferred should be supported via the Reactive adapter in Spring MVC, you could maybe wrap Coroutines code in async { } and just return the related Deferred return value. That's much better than runBlocking { }.

[pdegand]

hum, does this mean that I should be theorically able to return a Mono<> from a WebMVC controller as well ?
I should look into this “Reactive adapter”. Is this what’s described as HttpHandler in the doc ? https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-httphandler

[pdegand]

because I tried to change one of my WebMVC controller to return a Mono<>. But the body of the response was empty, even though, with logging, I knew that the Mono was being subscribed to

[sdeleuze]

Yes Mono should work as well

[sdeleuze]

If you do simple tests with returning Mono.just("foo) does it work ?

[pdegand]

Yes

[pdegand]

I had a OncePerRequestFilter that was preventing the body to be returned, when i removed it, it works fine when returning a Mono .

[pdegand]

But for coroutines, I can’t call async if I don’t have a scope. Is using GlobalScope inside a controller a good idea or should I stick with runBlocking ?

[sdeleuze]

Yes you can probably use GlobalScope.async { }

[pdegand]

👍

[pdegand]

Now I just need to find out why my RequestFilter is breaking the Reactive adapter

[Anders Mikkelsen]

If you check out mine and Jarle's talk from this years kotlinconf, you can see working examples of this, and pitfalls around it. If f.ex. you are using spring-security. runBlocking is a decent alternative in the itnerim, but ofc then everything is blocking, so it might not be worth it dependany on your use case.