PathApiVersionResolver registered before MediaTypeParamApiVersionResolver in auto-configuration

[srowatt]

Component: WebMvcAutoConfiguration.configureApiVersioningUse()

Issue: PathApiVersionResolver never returns null (as stated in its own Javadoc), so any resolvers added after it in the list are unreachable. Currently the media-type parameter resolver is added after the path-segment resolver.

Fix: Move map.from(use::getPathSegment).to(configurer::usePathSegment) to the end of the method, after the media-type parameter registration.

The following config will show the issue when the request is trying to use the media type to supply the API Version. Instead of trying the media type param resolver is tries the path resolver and then ends before trying the media type param resolve.

spring:
  mvc:   
    api-version:
      supported:
        - "1.0"
      use:
        header: "X-API-Version"
        query-parameter: "api-version"
        media-type-parameter:
          "[application/json]": "version"
          "[application/vnd.resource+json]": "version"
        path-segment: 0

[rstoyanchev]

Path versioning tends to be used exclusively because it's fixed in the path mappings, and clients must build the correct path.

I'm wondering if you have a specific case and if so could you elaborate?

For logical reasons, the path strategy could be made last in the order as it is not meant to yield, and I would recommend that for clarity, but it shouldn't make a difference in practice.

Note also a recent change spring-projects/spring-framework#36395 to support a Predicate<RequestPath> in the path resolver to decide if a given path is versioned. This is useful when some paths in the app aren't versioned, and it also means that now the strategy can return null, but only if given such a predicate. Having said that, I would still expect exclusive use of path versioning in a single app.