Allow locale to be overridden by "Accept-Language"

Previously, when `spring.mvc.locale` was specified, that locale was used
regardless of the client's preferences. This commit adds an extra
`spring.mvc.locale-resolver` property that can control how the locale is
resolved. The default is `ACCEPT_HEADER` but can be set to `FIXED` to
restore the previous behaviour.

Closes gh-6083

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

@@ -82,6 +82,7 @@ import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
 import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
+import org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver;
 import org.springframework.web.servlet.i18n.FixedLocaleResolver;
 import org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
@@ -103,6 +104,7 @@ import org.springframework.web.servlet.view.InternalResourceViewResolver;
  * @author Andy Wilkinson
  * @author Sébastien Deleuze
  * @author Eddú Meléndez
+ * @author Stephane Nicoll
  */
 @Configuration
 @ConditionalOnWebApplication
@@ -224,7 +226,14 @@ public class WebMvcAutoConfiguration {
 		@ConditionalOnMissingBean
 		@ConditionalOnProperty(prefix = "spring.mvc", name = "locale")
 		public LocaleResolver localeResolver() {
-			return new FixedLocaleResolver(this.mvcProperties.getLocale());
+			if (this.mvcProperties.getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {
+				return new FixedLocaleResolver(this.mvcProperties.getLocale());
+			}
+			else {
+				AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
+				localeResolver.setDefaultLocale(this.mvcProperties.getLocale());
+				return localeResolver;
+			}
 		}
 
 		@Bean

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/WebMvcProperties.java

@@ -42,10 +42,15 @@ public class WebMvcProperties {
 	private DefaultMessageCodesResolver.Format messageCodesResolverFormat;
 
 	/**
-	 * Locale to use.
+	 * Locale to use. By default, this locale is overridden by the "Accept-Language" header.
 	 */
 	private Locale locale;
 
+	/**
+	 * Define how the locale should be resolved.
+	 */
+	private LocaleResolver localeResolver = LocaleResolver.ACCEPT_HEADER;
+
 	/**
 	 * Date format to use (e.g. dd/MM/yyyy).
 	 */
@@ -105,6 +110,14 @@ public class WebMvcProperties {
 		this.locale = locale;
 	}
 
+	public LocaleResolver getLocaleResolver() {
+		return this.localeResolver;
+	}
+
+	public void setLocaleResolver(LocaleResolver localeResolver) {
+		this.localeResolver = localeResolver;
+	}
+
 	public String getDateFormat() {
 		return this.dateFormat;
 	}
@@ -240,4 +253,19 @@ public class WebMvcProperties {
 
 	}
 
+	public enum LocaleResolver {
+
+		/**
+		 * Always use the configured locale.
+		 */
+		FIXED,
+
+		/**
+		 * Use the "Accept-Language" header or the configured locale if the header
+		 * is not set.
+		 */
+		ACCEPT_HEADER
+
+	}
+
 }

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

@@ -49,6 +49,7 @@ import org.springframework.context.annotation.Import;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
 import org.springframework.format.support.FormattingConversionService;
+import org.springframework.http.HttpHeaders;
 import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.util.ReflectionUtils;
@@ -64,6 +65,7 @@ import org.springframework.web.servlet.ViewResolver;
 import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
 import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
+import org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver;
 import org.springframework.web.servlet.i18n.FixedLocaleResolver;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;
@@ -258,17 +260,45 @@ public class WebMvcAutoConfigurationTests {
 
 	@Test
 	public void overrideLocale() throws Exception {
-		load(AllResources.class, "spring.mvc.locale:en_UK");
+		load(AllResources.class, "spring.mvc.locale:en_UK",
+				"spring.mvc.locale-resolver=fixed");
 		// mock request and set user preferred locale
 		MockHttpServletRequest request = new MockHttpServletRequest();
 		request.addPreferredLocale(StringUtils.parseLocaleString("nl_NL"));
+		request.addHeader(HttpHeaders.ACCEPT_LANGUAGE, "nl_NL");
 		LocaleResolver localeResolver = this.context.getBean(LocaleResolver.class);
-		Locale locale = localeResolver.resolveLocale(request);
 		assertThat(localeResolver).isInstanceOf(FixedLocaleResolver.class);
+		Locale locale = localeResolver.resolveLocale(request);
 		// test locale resolver uses fixed locale and not user preferred locale
 		assertThat(locale.toString()).isEqualTo("en_UK");
 	}
 
+	@Test
+	public void useAcceptHeaderLocale() {
+		load(AllResources.class, "spring.mvc.locale:en_UK");
+		// mock request and set user preferred locale
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.addPreferredLocale(StringUtils.parseLocaleString("nl_NL"));
+		request.addHeader(HttpHeaders.ACCEPT_LANGUAGE, "nl_NL");
+		LocaleResolver localeResolver = this.context.getBean(LocaleResolver.class);
+		assertThat(localeResolver).isInstanceOf(AcceptHeaderLocaleResolver.class);
+		Locale locale = localeResolver.resolveLocale(request);
+		// test locale resolver uses user preferred locale
+		assertThat(locale.toString()).isEqualTo("nl_NL");
+	}
+
+	@Test
+	public void useDefaultLocaleIfAcceptHeaderNoSet() {
+		load(AllResources.class, "spring.mvc.locale:en_UK");
+		// mock request and set user preferred locale
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		LocaleResolver localeResolver = this.context.getBean(LocaleResolver.class);
+		assertThat(localeResolver).isInstanceOf(AcceptHeaderLocaleResolver.class);
+		Locale locale = localeResolver.resolveLocale(request);
+		// test locale resolver uses default locale if no header is set
+		assertThat(locale.toString()).isEqualTo("en_UK");
+	}
+
 	@Test
 	public void noDateFormat() throws Exception {
 		load(AllResources.class);

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -336,7 +336,8 @@ content into your application; rather pick only the properties that you need.
 	spring.mvc.dispatch-options-request=false # Dispatch OPTIONS requests to the FrameworkServlet doService method.
 	spring.mvc.favicon.enabled=true # Enable resolution of favicon.ico.
 	spring.mvc.ignore-default-model-on-redirect=true # If the content of the "default" model should be ignored during redirect scenarios.
-	spring.mvc.locale= # Locale to use.
+	spring.mvc.locale= # Locale to use. By default, this locale is overridden by the "Accept-Language" header.
+	spring.mvc.locale-resolver=accept-header # Define how the locale should be resolved.
 	spring.mvc.media-types.*= # Maps file extensions to media types for content negotiation.
 	spring.mvc.message-codes-resolver-format= # Formatting strategy for message codes. For instance `PREFIX_ERROR_CODE`.
 	spring.mvc.servlet.load-on-startup=-1 # Load on startup priority of the Spring Web Services servlet.