WebFlux: @ResponseStatus does not work out of the box, but ResponseStatusException does

[mmanciop]

As documented in https://github.com/mmanciop/response-status-repro, @ResponseStatus does not work out of the box with WebFlux applications, but ResponseStatusException does.

I think ResponseStatusException works and not @ResponseStatus due to org.springframework.boot.web.reactive.error.DefaultErrorAttributes#determineHttpStatus and other methods.

I truly cannot tell if this is by design or by oversight. Would it make sense for me to open a PR and add @ResponseStatus support to org.springframework.boot.web.reactive.error.DefaultErrorAttributes?

[philwebb]

I've dug into this a bit after upgrading the demo application to 2.1 and I think we have an ordering issue. Our DefaultErrorWebExceptionHandler is currently ordered -1 which means it ends up running before WebFluxResponseStatusExceptionHandler. This means the status detection logic never finds the correct code.

@bclozel What's the impact if we change the order at this stage?

[mmanciop]

Created a PR just in case it turns out it is better to just implement the support for @ResponseStatus in DefaultErrorWebExceptionHandler side-by-side with the support for ResponseStatusException.