Adds new ApiVersionCustomizer

[spencergibb]

This allows users to create beans to customize ApiVersionConfigurer.

[wilkinsona]

Thanks, @spencergibb.

I'm not fully up-to-speed on the background here, but this feels a little out of place to me when considering the WebMvcConfigurer contract and the various sub-configurers with which it's called.

Boot doesn't have customizers for:

• AsyncSupportConfigurer
• ContentNegotiationConfigurer
• PathMatchConfigurer

What's different about ApiVersionConfigurer that it needs an ApiVersionConfigurerCustomizer callback? Put another way, what capabilities does an ApiVersionConfigurerCustomizer unlock that aren't already available by defining an appropriately ordered WebMvcConfigurer that implements configureApiVersioning(ApiVersionConfigurer configurer)?

[spencergibb]

Spring Cloud Gateway would like to set the supportedVersionPredicate without totally overriding the boot configurer. I guessed a customizer bean was better than a predicate bean with a qualifier.

[wilkinsona]

The WebMvcConfigurers are additive so you can declare one alongside Boot's. Framework will then call each, giving them a change to configure the API version strategy. This means that you can already configure a predicate with a WebMvcConfigurer and make use of the property-based configuration at the same time:

	@Test
	void configureApiVersionStrategyWithPropertiesAndAdditionalWebMvcConfigurer() {
		Predicate<Comparable<?>> supportedVersionPredicate = (comparable) -> true;
		this.contextRunner.withPropertyValues("spring.mvc.apiversion.use.media-type-parameter[application/json]=mtpv")
			.withBean(WebMvcConfigurer.class, () -> new WebMvcConfigurer() {

				@Override
				public void configureApiVersioning(ApiVersionConfigurer configurer) {
					configurer.setSupportedVersionPredicate(supportedVersionPredicate);
				}

			})
			.run((context) -> {
				ApiVersionStrategy versionStrategy = context.getBean("mvcApiVersionStrategy", ApiVersionStrategy.class);
				assertThat(versionStrategy).extracting("supportedVersionPredicate")
					.isEqualTo(supportedVersionPredicate);
				MockHttpServletRequest request = new MockHttpServletRequest();
				request.addHeader(HttpHeaders.CONTENT_TYPE, "application/json;mtpv=123");
				assertThat(versionStrategy.resolveVersion(request)).isEqualTo("123");
			});
	}

[spencergibb]

I will try again. IIRC there was a duplicate bean error, but I will double check