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8159337: Introduce a method in Locale class to return the language tags as per RFC 5646 convention

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Reviewed-by: naoto, rriggs
This commit is contained in:
Justin Lu 2023-05-09 17:15:06 +00:00
parent 3aff5eacbd
commit 82bcee76ea
3 changed files with 276 additions and 5 deletions
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54
src/java.base/share/classes/java/util/Locale.java
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@ -1689,6 +1689,58 @@ public final class Locale implements Cloneable, Serializable {
return langTag;
}
/**
* {@return a case folded IETF BCP 47 language tag}
*
* <p>This method formats a language tag into one with case convention
* that adheres to section 2.1.1. Formatting of Language Tags of RFC5646.
* This format is defined as: <i>All subtags, including extension and private
* use subtags, use lowercase letters with two exceptions: two-letter
* and four-letter subtags that neither appear at the start of the tag
* nor occur after singletons. Such two-letter subtags are all
* uppercase (as in the tags "en-CA-x-ca" or "sgn-BE-FR") and four-
* letter subtags are titlecase (as in the tag "az-Latn-x-latn").</i> As
* legacy tags, (defined as "grandfathered" in RFC5646) are not always well-formed, this method
* will simply case fold a legacy tag to match the exact case convention
* for the particular tag specified in the respective
* {@link ##legacy_tags Legacy tags} table.
*
* <p><b>Special Exceptions</b>
* <p>To maintain consistency with {@link ##def_variant variant}
* which is case-sensitive, this method will neither case fold variant
* subtags nor case fold private use subtags prefixed by {@code lvariant}.
*
* <p>For example,
* {@snippet lang=java :
* String tag = "ja-kana-jp-x-lvariant-Oracle-JDK-Standard-Edition";
* Locale.caseFoldLanguageTag(tag); // returns "ja-Kana-JP-x-lvariant-Oracle-JDK-Standard-Edition"
* String tag2 = "ja-kana-jp-x-Oracle-JDK-Standard-Edition";
* Locale.caseFoldLanguageTag(tag2); // returns "ja-Kana-JP-x-oracle-jdk-standard-edition"
* }
*
* <p>Excluding case folding, this method makes no modifications to the tag itself.
* Case convention of language tags does not carry meaning, and is simply
* recommended as it corresponds with various ISO standards, including:
* ISO639-1, ISO15924, and ISO3166-1.
*
* <p>As the formatting of the case convention is dependent on the
* positioning of certain subtags, callers of this method should ensure
* that the language tag is well-formed, (conforming to section 2.1. Syntax
* of RFC5646).
*
* @param languageTag the IETF BCP 47 language tag.
* @throws IllformedLocaleException if {@code languageTag} is not well-formed
* @throws NullPointerException if {@code languageTag} is {@code null}
* @spec https://www.rfc-editor.org/rfc/rfc5646.html#section-2.1
* RFC5646 2.1. Syntax
* @spec https://www.rfc-editor.org/rfc/rfc5646#section-2.1.1
* RFC5646 2.1.1. Formatting of Language Tags
* @since 21
*/
public static String caseFoldLanguageTag(String languageTag) {
return LanguageTag.caseFoldTag(languageTag);
}
/**
* Returns a locale for the specified IETF BCP 47 language tag string.
*
@ -1748,7 +1800,7 @@ public final class Locale implements Cloneable, Serializable {
* // returns "th-TH-u-nu-thai-x-lvariant-TH"
* </pre></ul>
*
* <p>This implements the 'Language-Tag' production of BCP47, and
* <p id="legacy_tags">This implements the 'Language-Tag' production of BCP47, and
* so supports legacy (regular and irregular, referred to as
* "Type: grandfathered" in BCP47) as well as
* private use language tags. Stand alone private use tags are