Add set/getAcceptLanguage() to HttpHeaders

Issue: SPR-15024

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -20,6 +20,8 @@ import java.io.Serializable;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.nio.charset.Charset;
+import java.text.DecimalFormat;
+import java.text.DecimalFormatSymbols;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
@@ -37,6 +39,7 @@ import java.util.Set;
 import java.util.TimeZone;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedCaseInsensitiveMap;
@@ -384,6 +387,8 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 */
 	private static final Pattern ETAG_HEADER_VALUE_PATTERN = Pattern.compile("\\*|\\s*((W\\/)?(\"[^\"]*\"))\\s*,?");
 
+	private static final DecimalFormatSymbols DECIMAL_FORMAT_SYMBOLS = new DecimalFormatSymbols(Locale.ENGLISH);
+
 	private static TimeZone GMT = TimeZone.getTimeZone("GMT");
 
 
@@ -434,6 +439,34 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 		return MediaType.parseMediaTypes(get(ACCEPT));
 	}
 
+	/**
+	 * Set the acceptable language ranges,
+	 * as specified by the {@literal Accept-Language} header.
+	 * @see Locale.LanguageRange
+	 */
+	public void setAcceptLanguage(List<Locale.LanguageRange> languages) {
+		Assert.notNull(languages, "'languages' must not be null");
+		DecimalFormat df = new DecimalFormat("0.0", DECIMAL_FORMAT_SYMBOLS);
+		List<String> values = languages
+				.stream()
+				.map(r -> (r.getWeight() == Locale.LanguageRange.MAX_WEIGHT ? r.getRange() : r.getRange() + ";q=" + df.format(r.getWeight())))
+				.collect(Collectors.toList());
+		set(ACCEPT_LANGUAGE, toCommaDelimitedString(values));
+	}
+
+	/**
+	 * Return the acceptable language ranges,
+	 * as specified by the {@literal Accept-Language} header
+	 * @see Locale.LanguageRange
+	 */
+	public List<Locale.LanguageRange> getAcceptLanguage() {
+		String value = getFirst(ACCEPT_LANGUAGE);
+		if (value != null) {
+			return Locale.LanguageRange.parse(value);
+		}
+		return Collections.emptyList();
+	}
+
 	/**
 	 * Set the (new) value of the {@code Access-Control-Allow-Credentials} response header.
 	 */

spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java

@@ -422,4 +422,21 @@ public class HttpHeadersTests {
 		assertEquals(HttpMethod.POST, headers.getAccessControlRequestMethod());
 	}
 
+	@Test
+	public void acceptLanguage() {
+		assertTrue(headers.getAcceptLanguage().isEmpty());
+		String headerValue = "fr-ch, fr;q=0.9, en;q=0.8, de;q=0.7, *;q=0.5";
+		headers.setAcceptLanguage(Locale.LanguageRange.parse(headerValue));
+		assertEquals(headerValue, headers.getFirst(HttpHeaders.ACCEPT_LANGUAGE));
+		List<Locale.LanguageRange> languages = headers.getAcceptLanguage();
+		Locale.LanguageRange[] languageArray = new Locale.LanguageRange[]{
+				new Locale.LanguageRange("fr-ch"),
+				new Locale.LanguageRange("fr", 0.9),
+				new Locale.LanguageRange("en", 0.8),
+				new Locale.LanguageRange("de", 0.7),
+				new Locale.LanguageRange("*", 0.5)
+		};
+		assertArrayEquals(languageArray, languages.toArray());
+	}
+
 }