StringUtils.parseLocaleString detects variant without country

Includes tests for parsing all available locales on the JVM, checking toString/toLanguageTag equality between parsed and original locale.

Issue: SPR-7598
Issue: SPR-16651

spring-core/src/main/java/org/springframework/util/StringUtils.java

@@ -781,12 +781,15 @@ public abstract class StringUtils {
 
 	/**
 	 * Parse the given {@code String} representation into a {@link Locale}.
-	 * <p>This is the inverse operation of {@link Locale#toString Locale's toString}.
+	 * <p>For many parsing scenarios, this is an inverse operation of
+	 * {@link Locale#toString Locale's toString}, in a lenient sense.
+	 * This method does not aim for strict {@code Locale} design compliance;
+	 * it is rather specifically tailored for typical Spring parsing needs.
+	 * <p><b>Note: This delegate does not accept the BCP 47 language tag format.
+	 * Please use {@link #parseLocale} for lenient parsing of both formats.</b>
 	 * @param localeString the locale {@code String}: following {@code Locale's}
 	 * {@code toString()} format ("en", "en_UK", etc), also accepting spaces as
 	 * separators (as an alternative to underscores)
-	 * <p>Note: This variant does not accept the BCP 47 language tag format.
-	 * Please use {@link #parseLocale} for lenient parsing of both formats.
 	 * @return a corresponding {@code Locale} instance, or {@code null} if none
 	 * @throws IllegalArgumentException in case of an invalid locale specification
 	 */
@@ -817,6 +820,12 @@ public abstract class StringUtils {
 				variant = trimLeadingCharacter(variant, '_');
 			}
 		}
+
+		if ("".equals(variant) && country.startsWith("#")) {
+			variant = country;
+			country = "";
+		}
+
 		return (language.length() > 0 ? new Locale(language, country, variant) : null);
 	}
 

spring-core/src/test/java/org/springframework/util/StringUtilsTests.java

@@ -734,9 +734,35 @@ public class StringUtilsTests {
 		assertEquals("Variant containing country code not extracted correctly", variant, locale.getVariant());
 	}
 
-	@Test  // SPR-14718
+	@Test  // SPR-14718, SPR-7598
 	public void testParseJava7Variant() {
-		assertEquals("sr_#LATN", StringUtils.parseLocaleString("sr_#LATN").toString());
+		assertEquals("sr__#LATN", StringUtils.parseLocaleString("sr__#LATN").toString());
+	}
+
+	@Test  // SPR-16651
+	public void testAvailableLocalesWithLocaleString() {
+		for (Locale locale : Locale.getAvailableLocales()) {
+			Locale parsedLocale = StringUtils.parseLocaleString(locale.toString());
+			if (parsedLocale == null) {
+				assertEquals("", locale.getLanguage());
+			}
+			else {
+				assertEquals(parsedLocale.toString(), locale.toString());
+			}
+		}
+	}
+
+	@Test  // SPR-16651
+	public void testAvailableLocalesWithLanguageTag() {
+		for (Locale locale : Locale.getAvailableLocales()) {
+			Locale parsedLocale = StringUtils.parseLocale(locale.toLanguageTag());
+			if (parsedLocale == null) {
+				assertEquals("", locale.getLanguage());
+			}
+			else {
+				assertEquals(parsedLocale.toLanguageTag(), locale.toLanguageTag());
+			}
+		}
 	}
 
 }