Require bean name match for Locale(Context)Resolver to back off

Web MVC and WebFlux look up by name the Locale(Context)Resolver beans
that they use. Previously, the auto-configured resolvers for MVC and
WebFlux would back off when any bean of the required type was defined,
irrespective of its name. If the name of the user's bean didn't match
the name used by MVC and WebFlux to find the custom resolver, the
custom resolver would be ignored and MVC and WebFlux would use their
defaults. There was no indication of this happening in the condition
evaluation report as all it would show is that the auto-configured
resolver had backed off in favour of the custom resolver. It wouldn't
show anything to explain why the custom resolver had not been used.

This commit updates the auto-configured resolvers to be conditional
on a missing bean of the name required by MVC and WebFlux. If the
user then defines a custom resolver with a different name, the
condition evaluation report will show that the auto-configured
resolver remained as the bean name didn't match.

Fixes gh-24209

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfiguration.java

@@ -70,6 +70,7 @@
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerAdapter;
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerMapping;
 import org.springframework.web.reactive.result.view.ViewResolver;
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
 import org.springframework.web.server.i18n.AcceptHeaderLocaleContextResolver;
 import org.springframework.web.server.i18n.FixedLocaleContextResolver;
 import org.springframework.web.server.i18n.LocaleContextResolver;
@@ -289,7 +290,7 @@ protected RequestMappingHandlerMapping createRequestMappingHandlerMapping() {
 
 		@Bean
 		@Override
-		@ConditionalOnMissingBean
+		@ConditionalOnMissingBean(name = WebHttpHandlerBuilder.LOCALE_CONTEXT_RESOLVER_BEAN_NAME)
 		public LocaleContextResolver localeContextResolver() {
 			if (this.webProperties.getLocaleResolver() == WebProperties.LocaleResolver.FIXED) {
 				return new FixedLocaleContextResolver(this.webProperties.getLocale());

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration.java

@@ -441,7 +441,7 @@ public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext ap
 
 		@Override
 		@Bean
-		@ConditionalOnMissingBean
+		@ConditionalOnMissingBean(name = DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME)
 		@SuppressWarnings("deprecation")
 		public LocaleResolver localeResolver() {
 			if (this.webProperties.getLocaleResolver() == WebProperties.LocaleResolver.FIXED) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfigurationTests.java

@@ -79,6 +79,7 @@
 import org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerMapping;
 import org.springframework.web.reactive.result.view.ViewResolutionResultHandler;
 import org.springframework.web.reactive.result.view.ViewResolver;
+import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.i18n.AcceptHeaderLocaleContextResolver;
 import org.springframework.web.server.i18n.FixedLocaleContextResolver;
 import org.springframework.web.server.i18n.LocaleContextResolver;
@@ -531,10 +532,25 @@ void whenAcceptHeaderLocaleContextResolverIsUsedAndHeaderIsAbsentThenConfiguredL
 	}
 
 	@Test
-	void customLocaleContextResolver() {
-		this.contextRunner.withUserConfiguration(LocaleContextResolverConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(LocaleContextResolver.class)
-						.hasBean("customLocaleContextResolver"));
+	void customLocaleContextResolverWithMatchingNameReplacedAutoConfiguredLocaleContextResolver() {
+		this.contextRunner
+				.withBean("localeContextResolver", CustomLocaleContextResolver.class, CustomLocaleContextResolver::new)
+				.run((context) -> {
+					assertThat(context).hasSingleBean(LocaleContextResolver.class);
+					assertThat(context.getBean("localeContextResolver"))
+							.isInstanceOf(CustomLocaleContextResolver.class);
+				});
+	}
+
+	@Test
+	void customLocaleContextResolverWithDifferentNameDoesNotReplaceAutoConfiguredLocaleContextResolver() {
+		this.contextRunner.withBean("customLocaleContextResolver", CustomLocaleContextResolver.class,
+				CustomLocaleContextResolver::new).run((context) -> {
+					assertThat(context.getBean("customLocaleContextResolver"))
+							.isInstanceOf(CustomLocaleContextResolver.class);
+					assertThat(context.getBean("localeContextResolver"))
+							.isInstanceOf(AcceptHeaderLocaleContextResolver.class);
+				});
 	}
 
 	private Map<PathPattern, Object> getHandlerMap(ApplicationContext context) {
@@ -767,12 +783,15 @@ public Example parse(String source, Locale locale) {
 
 	}
 
-	@Configuration(proxyBeanMethods = false)
-	static class LocaleContextResolverConfiguration {
+	static class CustomLocaleContextResolver implements LocaleContextResolver {
 
-		@Bean
-		LocaleContextResolver customLocaleContextResolver() {
-			return new AcceptHeaderLocaleContextResolver();
+		@Override
+		public LocaleContext resolveLocaleContext(ServerWebExchange exchange) {
+			return () -> Locale.ENGLISH;
+		}
+
+		@Override
+		public void setLocaleContext(ServerWebExchange exchange, LocaleContext localeContext) {
 		}
 
 	}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfigurationTests.java

@@ -344,6 +344,24 @@ void useDefaultLocaleIfAcceptHeaderNoSet(String mvcOrWeb) {
 		});
 	}
 
+	@Test
+	void customLocaleResolverWithMatchingNameReplacesAutoConfiguredLocaleResolver() {
+		this.contextRunner.withBean("localeResolver", CustomLocaleResolver.class, CustomLocaleResolver::new)
+				.run((context) -> {
+					assertThat(context).hasSingleBean(LocaleResolver.class);
+					assertThat(context.getBean("localeResolver")).isInstanceOf(CustomLocaleResolver.class);
+				});
+	}
+
+	@Test
+	void customLocaleResolverWithDifferentNameDoesNotReplaceAutoConfiguredLocaleResolver() {
+		this.contextRunner.withBean("customLocaleResolver", CustomLocaleResolver.class, CustomLocaleResolver::new)
+				.run((context) -> {
+					assertThat(context.getBean("customLocaleResolver")).isInstanceOf(CustomLocaleResolver.class);
+					assertThat(context.getBean("localeResolver")).isInstanceOf(AcceptHeaderLocaleResolver.class);
+				});
+	}
+
 	@Test
 	void defaultDateFormat() {
 		this.contextRunner.run((context) -> {
@@ -1376,4 +1394,17 @@ ServletRegistrationBean<?> additionalDispatcherServlet() {
 
 	}
 
+	static class CustomLocaleResolver implements LocaleResolver {
+
+		@Override
+		public Locale resolveLocale(HttpServletRequest request) {
+			return Locale.ENGLISH;
+		}
+
+		@Override
+		public void setLocale(HttpServletRequest request, HttpServletResponse response, Locale locale) {
+		}
+
+	}
+
 }