Handle trailing semicolon in Accept-Language

Closes gh-32259

Author: poutsma

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

@@ -509,7 +509,20 @@ public void setAcceptLanguage(List<Locale.LanguageRange> languages) {
 	 */
 	public List<Locale.LanguageRange> getAcceptLanguage() {
 		String value = getFirst(ACCEPT_LANGUAGE);
-		return (StringUtils.hasText(value) ? Locale.LanguageRange.parse(value) : Collections.emptyList());
+		if (StringUtils.hasText(value)) {
+			try {
+				return Locale.LanguageRange.parse(value);
+			}
+			catch (IllegalArgumentException ignored) {
+				String[] tokens = StringUtils.tokenizeToStringArray(value, ",");
+				for (int i = 0; i < tokens.length; i++) {
+					tokens[i] = StringUtils.trimTrailingCharacter(tokens[i], ';');
+				}
+				value = StringUtils.arrayToCommaDelimitedString(tokens);
+				return Locale.LanguageRange.parse(value);
+			}
+		}
+		return Collections.emptyList();
 	}
 
 	/**

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

@@ -517,6 +517,20 @@ void acceptLanguage() {
 		assertThat(headers.getAcceptLanguageAsLocales()).first().isEqualTo(Locale.FRANCE);
 	}
 
+	@Test // gh-32259
+	void acceptLanguageTrailingSemicolon() {
+		String headerValue = "en-us,en;,nl;";
+		headers.set(HttpHeaders.ACCEPT_LANGUAGE, headerValue);
+		assertThat(headers.getFirst(HttpHeaders.ACCEPT_LANGUAGE)).isEqualTo(headerValue);
+
+		List<Locale.LanguageRange> expectedRanges = Arrays.asList(
+				new Locale.LanguageRange("en-us"),
+				new Locale.LanguageRange("en"),
+				new Locale.LanguageRange("nl")
+		);
+		assertThat(headers.getAcceptLanguage()).isEqualTo(expectedRanges);
+	}
+
 	@Test // SPR-15603
 	void acceptLanguageWithEmptyValue() {
 		this.headers.set(HttpHeaders.ACCEPT_LANGUAGE, "");