Auto-configure Spring Data's reactive method argument resolvers in a reactive web application

[cbornet]

Spring Data now has argument resolvers for Pageable and Sort for Webflux.
It would be great to have these autoconfigured if spring-data-commons is detected on the classpath like what is done for MVC.
From the discussion with @mp911de (spring-projects/spring-data-commons#264 (comment)), could you give advice on where it's best to provide the configuration components (esp. the creation of the resolver beans and their customizers) ?
I can work on this once settled if you want.

[wilkinsona]

I suspect that there's some subtlety to this that I am missing. On the face of it, it would seem pretty straightforward for us to add configuration that is similar to the following:

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ReactiveSortHandlerMethodArgumentResolver.class)
@ConditionalOnWebApplication(type = Type.REACTIVE)
public class SpringDataWebFluxAutoConfiguration {

    @Bean
    WebFluxConfigurer springDataArgumentResolversConfigurer() {
        return new WebFluxConfigurer() {

            @Override
            public void configureArgumentResolvers(ArgumentResolverConfigurer configurer) {
                configurer.addCustomResolver(new ReactiveSortHandlerMethodArgumentResolver(),
                        new ReactivePageableHandlerMethodArgumentResolver());
            }

        };
    }

}

[mp911de]

I was cautious as @gregturn is working on improved configuration support for WebFlux from a Spring HATEOAS perspective. Given the proximity of this issue towards Spring Data REST I wanted to make sure to keep everyone involved in the loop and to not come up with an implementation that would contradict with ideas that are evolving around other config API in Spring HATEOAS/Spring Data REST.

[gregturn]

This is what Spring HATEOAS does (register a WebFluxConfigurer).

https://github.com/spring-projects/spring-hateoas/blob/master/src/main/java/org/springframework/hateoas/config/WebFluxHateoasConfiguration.java#L79-L94

I'm not sure if this is a collision with what Spring Data Commons is doing, or not.

[wilkinsona]

Thanks, both. I can't see any danger of a clash based on that. It looks to me like we can safely add some auto-configuration like that in my earlier comment.

[cbornet]

Spring MVC has customizers for these resolvers. Maybe they should also be added for Webflux ?

[wilkinsona]

@cbornet Sorry, I don't understand what you're suggesting. What Spring MVC customisers are you referring to?

[cbornet]

I'm referring to the customizers in SpringDataWebConfiguration : PageableHandlerMethodArgumentResolverCustomizer and SortHandlerMethodArgumentResolverCustomizer

[wilkinsona]

Thanks. FWIW, those are part of Spring Data rather than Spring MVC.

The customizers make sense for Spring Data's web support on a Servlet-based stack as it provides a way to customise the argument resolvers that are automatically defined by SpringDataWebConfiguration.

I'm changing my mind about the issue now. It's not clear to me why Spring Data Commons cannot provide a WebFlux equivalent of @EnableSpringDataWebSupport. It looks to me like a lot, if not all, of what it does would also be applicable to a WebFlux-based app that's rolling its own @RestControllers and making use of reactive Spring Data repositories.

If Spring Data Commons did this, we could then customise the reactive argument resolvers that it defines via a similar mechanism to that used today for the Servlet/MVC side of things.