MockHttpServletRequest restores default locale for empty accept header

Closes gh-22877

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletRequest.java

 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -199,7 +199,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	private String remoteHost = DEFAULT_REMOTE_HOST;
 
 	/** List of locales in descending order. */
-	private final List<Locale> locales = new LinkedList<>();
+	private final LinkedList<Locale> locales = new LinkedList<>();
 
 	private boolean secure = false;
 
@@ -403,12 +403,11 @@ public class MockHttpServletRequest implements HttpServletRequest {
 
 	private void updateContentTypeHeader() {
 		if (StringUtils.hasLength(this.contentType)) {
-			StringBuilder sb = new StringBuilder(this.contentType);
-			if (!this.contentType.toLowerCase().contains(CHARSET_PREFIX) &&
-					StringUtils.hasLength(this.characterEncoding)) {
-				sb.append(";").append(CHARSET_PREFIX).append(this.characterEncoding);
+			String value = this.contentType;
+			if (StringUtils.hasLength(this.characterEncoding) && !this.contentType.toLowerCase().contains(CHARSET_PREFIX)) {
+				value += ';' + CHARSET_PREFIX + this.characterEncoding;
 			}
-			doAddHeaderValue(HttpHeaders.CONTENT_TYPE, sb.toString(), true);
+			doAddHeaderValue(HttpHeaders.CONTENT_TYPE, value, true);
 		}
 	}
 
@@ -780,7 +779,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	 */
 	public void addPreferredLocale(Locale locale) {
 		Assert.notNull(locale, "Locale must not be null");
-		this.locales.add(0, locale);
+		this.locales.addFirst(locale);
 		updateAcceptLanguageHeader();
 	}
 
@@ -818,7 +817,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	 */
 	@Override
 	public Locale getLocale() {
-		return this.locales.get(0);
+		return this.locales.getFirst();
 	}
 
 	/**
@@ -1016,6 +1015,9 @@ public class MockHttpServletRequest implements HttpServletRequest {
 				List<Locale> locales = headers.getAcceptLanguageAsLocales();
 				this.locales.clear();
 				this.locales.addAll(locales);
+				if (this.locales.isEmpty()) {
+					this.locales.add(Locale.ENGLISH);
+				}
 			}
 			catch (IllegalArgumentException ex) {
 				// Invalid Accept-Language format -> just store plain header

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletRequestTests.java

 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -351,6 +351,13 @@ public class MockHttpServletRequestTests {
 		assertEquals("en_US", request.getHeader("Accept-Language"));
 	}
 
+	@Test
+	public void emptyAcceptLanguageHeader() {
+		request.addHeader("Accept-Language", "");
+		assertEquals(Locale.ENGLISH, request.getLocale());
+		assertEquals("", request.getHeader("Accept-Language"));
+	}
+
 	@Test
 	public void getServerNameWithDefaultName() {
 		assertEquals("localhost", request.getServerName());

spring-web/src/test/java/org/springframework/mock/web/test/MockHttpServletRequest.java

 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -199,7 +199,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	private String remoteHost = DEFAULT_REMOTE_HOST;
 
 	/** List of locales in descending order. */
-	private final List<Locale> locales = new LinkedList<>();
+	private final LinkedList<Locale> locales = new LinkedList<>();
 
 	private boolean secure = false;
 
@@ -403,12 +403,11 @@ public class MockHttpServletRequest implements HttpServletRequest {
 
 	private void updateContentTypeHeader() {
 		if (StringUtils.hasLength(this.contentType)) {
-			StringBuilder sb = new StringBuilder(this.contentType);
-			if (!this.contentType.toLowerCase().contains(CHARSET_PREFIX) &&
-					StringUtils.hasLength(this.characterEncoding)) {
-				sb.append(";").append(CHARSET_PREFIX).append(this.characterEncoding);
+			String value = this.contentType;
+			if (StringUtils.hasLength(this.characterEncoding) && !this.contentType.toLowerCase().contains(CHARSET_PREFIX)) {
+				value += ';' + CHARSET_PREFIX + this.characterEncoding;
 			}
-			doAddHeaderValue(HttpHeaders.CONTENT_TYPE, sb.toString(), true);
+			doAddHeaderValue(HttpHeaders.CONTENT_TYPE, value, true);
 		}
 	}
 
@@ -780,7 +779,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	 */
 	public void addPreferredLocale(Locale locale) {
 		Assert.notNull(locale, "Locale must not be null");
-		this.locales.add(0, locale);
+		this.locales.addFirst(locale);
 		updateAcceptLanguageHeader();
 	}
 
@@ -818,7 +817,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	 */
 	@Override
 	public Locale getLocale() {
-		return this.locales.get(0);
+		return this.locales.getFirst();
 	}
 
 	/**
@@ -1016,6 +1015,9 @@ public class MockHttpServletRequest implements HttpServletRequest {
 				List<Locale> locales = headers.getAcceptLanguageAsLocales();
 				this.locales.clear();
 				this.locales.addAll(locales);
+				if (this.locales.isEmpty()) {
+					this.locales.add(Locale.ENGLISH);
+				}
 			}
 			catch (IllegalArgumentException ex) {
 				// Invalid Accept-Language format -> just store plain header