AcceptHeaderLocaleResolver returns default locale in case of no supported locale found

Issue: SPR-15426
(cherry picked from commit ea98ee8)

spring-webmvc/src/main/java/org/springframework/web/servlet/i18n/AcceptHeaderLocaleResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -95,11 +95,15 @@ public class AcceptHeaderLocaleResolver implements LocaleResolver {
 		if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
 			return defaultLocale;
 		}
-		Locale locale = request.getLocale();
-		if (!isSupportedLocale(locale)) {
-			locale = findSupportedLocale(request, locale);
+		Locale requestLocale = request.getLocale();
+		if (isSupportedLocale(requestLocale)) {
+			return requestLocale;
 		}
-		return locale;
+		Locale supportedLocale = findSupportedLocale(request);
+		if (supportedLocale != null) {
+			return supportedLocale;
+		}
+		return (defaultLocale != null ? defaultLocale : requestLocale);
 	}
 
 	private boolean isSupportedLocale(Locale locale) {
@@ -107,7 +111,7 @@ public class AcceptHeaderLocaleResolver implements LocaleResolver {
 		return (supportedLocales.isEmpty() || supportedLocales.contains(locale));
 	}
 
-	private Locale findSupportedLocale(HttpServletRequest request, Locale fallback) {
+	private Locale findSupportedLocale(HttpServletRequest request) {
 		Enumeration<Locale> requestLocales = request.getLocales();
 		while (requestLocales.hasMoreElements()) {
 			Locale locale = requestLocales.nextElement();
@@ -115,7 +119,7 @@ public class AcceptHeaderLocaleResolver implements LocaleResolver {
 				return locale;
 			}
 		}
-		return fallback;
+		return null;
 	}
 
 	@Override

spring-webmvc/src/test/java/org/springframework/web/servlet/i18n/AcceptHeaderLocaleResolverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.web.servlet.i18n;
 
 import java.util.Arrays;
@@ -24,15 +25,14 @@ import org.junit.Test;
 
 import org.springframework.mock.web.test.MockHttpServletRequest;
 
-import static java.util.Locale.CANADA;
-import static java.util.Locale.JAPANESE;
-import static java.util.Locale.UK;
-import static java.util.Locale.US;
-import static org.junit.Assert.assertEquals;
+import static java.util.Locale.*;
+import static org.junit.Assert.*;
 
 /**
  * Unit tests for {@link AcceptHeaderLocaleResolver}.
+ *
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  */
 public class AcceptHeaderLocaleResolverTests {
 
@@ -56,6 +56,17 @@ public class AcceptHeaderLocaleResolverTests {
 		this.resolver.setSupportedLocales(Collections.singletonList(CANADA));
 		assertEquals(US, this.resolver.resolveLocale(request(US, UK)));
 	}
+	@Test
+
+	public void resolvePreferredNotSupportedWithDefault() {
+		this.resolver.setSupportedLocales(Arrays.asList(US, JAPAN));
+		this.resolver.setDefaultLocale(Locale.JAPAN);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.addHeader("Accept-Language", KOREA.toString());
+		request.setPreferredLocales(Collections.singletonList(KOREA));
+		assertEquals(Locale.JAPAN, this.resolver.resolveLocale(request));
+	}
 
 	@Test
 	public void defaultLocale() throws Exception {