The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
The Java Programming language contains internationalization support for language tags, language tag filtering, and language tag lookup. These features are specified by IETF BCP 47 , which contains RFC 5646 "Tags for Identifying Languages" and RFC 4647 "Matching of Language Tags." This lesson describes how this support is provided in the JDK.
Language tags are specially formatted strings that provide information about a particular language. A language tag might be something simple (such as "en" for English), something complex (such as "zh-cmn-Hans-CN" for Chinese, Mandarin, Simplified script, as used in China), or something in between (such as "sr-Latn", for Serbian written using Latin script). Language tags consist of "subtags" separated by hyphens; this terminology is used throughout the API documentation.
The
java.util.Locale
class provides support for language tags. A Locale
contains several different fields: language (such as "en" for English, or "ja" for Japanese), script (such as "Latn" for Latin or "Cyrl" for Cyrillic), country (such as "US" for United States or "FR" for France), variant (which indicates some variant of a locale), and extensions (which provides a map of single character keys to String
values, indicating extensions apart from language identification).
To create a Locale
object from a language tag String
, invoke
Locale.forLanguageTag(String)
, passing in the language tag as its only argument. Doing so creates and returns a new Locale
object for use in your application.
Example 1:
package languagetagdemo; import java.util.Locale; public class LanguageTagDemo { public static void main(String[] args) { Locale l = Locale.forLanguageTag("en-US"); } }
Note that the Locale API only requires that your language tag be syntactically well-formed. It does not perform any extra validation (such as checking to see if the tag is registered in the IANA Language Subtag Registry).
Language ranges (represented by class
java.util.Locale.LanguageRange
) identify sets of language tags that share specific attributes. Language ranges are classified as either basic or extended, and are similar to language tags in that they consist of subtags separated by hyphens. Examples of basic language ranges include "en" (English), "ja-JP" (Japanese, Japan), and "*" (a special language range which matches any language tag). Examples of extended language ranges include "*-CH" (any language, Switzerland), "es-*" (Spanish, any regions), and "zh-Hant-*" (Traditional Chinese, any region).
Furthermore, language ranges may be stored in Language Priority Lists, which enable users to prioritize their language preferences in a weighted list. Language Priority Lists are expressed by placing LanguageRange
objects into a
java.util.List
, which can then be passed to the Locale
methods that accept a List
of LanguageRange
objects.
The
Locale.LanguageRange
class provides two different constructors for creating language ranges:
public Locale.LanguageRange(String range)
public Locale.LanguageRange(String range, double weight)
The only difference between them is that the second version allows a weight to be specified; this weight will be considered if the range is placed into a Language Priority List.
Locale.LanguageRange
also specifies some constants to be used with these constructors:
public static final double MAX_WEIGHT
public static final double MIN_WEIGHT
The MAX_WEIGHT
constant holds a value of 1.0, which indicates that it is a good fit for the user. The MIN_WEIGHT
constant holds a value of 0.0, indicating that it is not.
Example 2:
package languagetagdemo; import java.util.Locale; public class LanguageTagDemo { public static void main(String[] args) { // Create Locale Locale l = Locale.forLanguageTag("en-US"); // Define Some LanguageRange Objects Locale.LanguageRange range1 = new Locale.LanguageRange("en-US",Locale.LanguageRange.MAX_WEIGHT); Locale.LanguageRange range2 = new Locale.LanguageRange("en-GB*",0.5); Locale.LanguageRange range3 = new Locale.LanguageRange("fr-FR",Locale.LanguageRange.MIN_WEIGHT); } }
Example 2 creates three language ranges: English (United States), English (Great Britain), and French (France). These ranges are weighted to express the user's preferences, in order from most preferred to least preferred.
You can create a Language Priority List from a list of language ranges
by using the
LanguageRange.parse(String)
method. This method accepts a
list of comma-separated language ranges, performs a syntactic check for
each language range in the given ranges, and then returns the newly
created Language Priority List.
For detailed information about the required format of the "ranges" parameter, see the API specification for this method.
Example 3:
package languagetagdemo; import java.util.Locale; import java.util.List; public class LanguageTagDemo { public static void main(String[] args) { // Create Locale Locale l = Locale.forLanguageTag("en-US"); // Create a Language Priority List String ranges = "en-US;q=1.0,en-GB;q=0.5,fr-FR;q=0.0"; List<Locale.LanguageRange> languageRanges = Locale.LanguageRange.parse(ranges) } }
Example 3 creates the same three language ranges as Example 2, but
stores them in a String
object, which is passed to the parse(String)
method. The returned List
of LanguageRange
objects is the Language
Priority List.
Language tag filtering is the process of matching a set of language tags against a user's Language Priority List. The result of filtering will be a complete list of all matching results. The Locale
class defines two filter methods that return a list of Locale
objects. Their signatures are as follows:
public static List<Locale> filter (List<Locale.LanguageRange> priorityList, Collection<Locale> locales)
public static List<Locale> filter (List<Locale.LanguageRange> priorityList, Collection<Locale> locales, Locale.FilteringMode mode)
In both methods, the first argument specifies the user's Language Priority List as described in the previous section.
The second argument specifies a Collection
of Locale
objects to match against.
The match itself will take place according to the rules specified by RFC 4647.
The third argument (if provided) specifies the "filtering mode" to use. The
Locale.FilteringMode
enum provides a number of different values to choose from, such as AUTOSELECT_FILTERING
(for basic language range filtering) or EXTENDED_FILTERING
(for extended language range filtering).
Example 4 provides a demonstration of language tag filtering.
Example 4:
package languagetagdemo; import java.util.Locale; import java.util.Collection; import java.util.List; import java.util.ArrayList; public class LanguageTagDemo { public static void main(String[] args) { // Create a collection of Locale objects to filter Collection<Locale> locales = new ArrayList<>(); locales.add(Locale.forLanguageTag("en-GB")); locales.add(Locale.forLanguageTag("ja")); locales.add(Locale.forLanguageTag("zh-cmn-Hans-CN")); locales.add(Locale.forLanguageTag("en-US")); // Express the user's preferences with a Language Priority List String ranges = "en-US;q=1.0,en-GB;q=0.5,fr-FR;q=0.0"; List<Locale.LanguageRange> languageRanges = Locale.LanguageRange.parse(ranges); // Now filter the Locale objects, returning any matches List<Locale> results = Locale.filter(languageRanges,locales); // Print out the matches for(Locale l : results){ System.out.println(l.toString()); } } }
The output of this program is:
en_US
en_GB
This returned list is ordered according to the weights specified in the user's Language Priority List.
The Locale
class also defines filterTags
methods for filtering language tags as String
objects.
The method signatures are as follows:
public static List<String> filterTags (List<Locale.LanguageRange> priorityList, Collection<String> tags)
public static List<String> filterTags (List<Locale.LanguageRange> priorityList, Collection<String> tags, Locale.FilteringMode mode)
Example 5 provides the same search as Example 4, but uses String
objects instead of Locale
objects.
Example 5:
package languagetagdemo; import java.util.Locale; import java.util.Collection; import java.util.List; import java.util.ArrayList; public class LanguageTagDemo { public static void main(String[] args) { // Create a collection of String objects to match against Collection<String> tags = new ArrayList<>(); tags.add("en-GB"); tags.add("ja"); tags.add("zh-cmn-Hans-CN"); tags.add("en-US"); // Express user's preferences with a Language Priority List String ranges = "en-US;q=1.0,en-GB;q=0.5,fr-FR;q=0.0"; List<Locale.LanguageRange> languageRanges = Locale.LanguageRange.parse(ranges); // Now search the locales for the best match List<String> results = Locale.filterTags(languageRanges,tags); // Print out the matches for(String s : results){ System.out.println(s); } } }
As before, the search will match and return "en-US" and "en-GB" (in that order).
In contrast to language tag filtering, language tag lookup is the process of matching language ranges to sets of language tags and returning the one language tag that best matches the range. RFC4647 states that: "Lookup produces the single result that best matches the user's preferences from the list of available tags, so it is useful in cases in which a single item is required (and for which only a single item can be returned). For example, if a process were to insert a human-readable error message into a protocol header, it might select the text based on the user's language priority list. Since the process can return only one item, it is forced to choose a single item and it has to return some item, even if none of the content's language tags match the language priority list supplied by the user."
Example 6:
package languagetagdemo; import java.util.Locale; import java.util.Collection; import java.util.List; import java.util.ArrayList; public class LanguageTagDemo { public static void main(String[] args) { // Create a collection of Locale objects to search Collection<Locale> locales = new ArrayList<>(); locales.add(Locale.forLanguageTag("en-GB")); locales.add(Locale.forLanguageTag("ja")); locales.add(Locale.forLanguageTag("zh-cmn-Hans-CN")); locales.add(Locale.forLanguageTag("en-US")); // Express the user's preferences with a Language Priority List String ranges = "en-US;q=1.0,en-GB;q=0.5,fr-FR;q=0.0"; List<Locale.LanguageRange> languageRanges = Locale.LanguageRange.parse(ranges); // Find the BEST match, and return just one result Locale result = Locale.lookup(languageRanges,locales); System.out.println(result.toString()); } }
In contrast to the filtering examples, the lookup demo in Example 6 returns the one object that is the best match (en-US
in this case). For completeness, Example 7 shows how to perform the same lookup using String
objects.
Example 7:
package languagetagdemo; import java.util.Locale; import java.util.Collection; import java.util.List; import java.util.ArrayList; public class LanguageTagDemo { public static void main(String[] args) { // Create a collection of String objects to match against Collection<String> tags = new ArrayList<>(); tags.add("en-GB"); tags.add("ja"); tags.add("zh-cmn-Hans-CN"); tags.add("en-US"); // Express user's preferences with a Language Priority List String ranges = "en-US;q=1.0,en-GB;q=0.5,fr-FR;q=0.0"; List<Locale.LanguageRange> languageRanges = Locale.LanguageRange.parse(ranges); // Find the BEST match, and return just one result String result = Locale.lookupTag(languageRanges, tags); System.out.println(result); } }
This example returns the single object that best matches the user's Language Priority List.