LocaleUtils
Date: 2017-02-08

org.apache.commons.lang3

## Class LocaleUtils

- java.lang.Object
- - org.apache.commons.lang3.LocaleUtils

-     public class LocaleUtils
      extends java.lang.Object

  Operations to assist when working with a `Locale`.

  This class tries to handle `null` input gracefully. An exception will not be thrown for a `null` input. Each method documents its behaviour in more detail.

  Since:
    2.2

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `LocaleUtils()` `LocaleUtils` instances should NOT be constructed in standard programming.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static java.util.List<java.util.Locale>` | `availableLocaleList()` Obtains an unmodifiable list of installed locales.
    `static java.util.Set<java.util.Locale>` | `availableLocaleSet()` Obtains an unmodifiable set of installed locales.
    `static java.util.List<java.util.Locale>` | `countriesByLanguage(java.lang.String languageCode)` Obtains the list of countries supported for a given language.
    `static boolean` | `isAvailableLocale(java.util.Locale locale)` Checks if the locale specified is in the list of available locales.
    `static java.util.List<java.util.Locale>` | `languagesByCountry(java.lang.String countryCode)` Obtains the list of languages supported for a given country.
    `static java.util.List<java.util.Locale>` | `localeLookupList(java.util.Locale locale)` Obtains the list of locales to search through when performing a locale search.
    `static java.util.List<java.util.Locale>` | `localeLookupList(java.util.Locale locale, java.util.Locale defaultLocale)` Obtains the list of locales to search through when performing a locale search.
    `static java.util.Locale` | `toLocale(java.lang.String str)` Converts a String to a Locale.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### LocaleUtils

          public LocaleUtils()

      `LocaleUtils` instances should NOT be constructed in standard programming. Instead, the class should be used as `LocaleUtils.toLocale("en_GB");`.

      This constructor is public to permit tools that require a JavaBean instance to operate.

  - ### Method Detail

    - #### toLocale

          public static java.util.Locale toLocale(java.lang.String str)

      Converts a String to a Locale.

      This method takes the string format of a locale and creates the locale object from it.

             LocaleUtils.toLocale("")           = new Locale("", "")
             LocaleUtils.toLocale("en")         = new Locale("en", "")
             LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")
             LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)

      (#) The behaviour of the JDK variant constructor changed between JDK1.3 and JDK1.4. In JDK1.3, the constructor upper cases the variant, in JDK1.4, it doesn't. Thus, the result from getVariant() may vary depending on your JDK.

      This method validates the input strictly. The language code must be lowercase. The country code must be uppercase. The separator must be an underscore. The length must be correct.

      Parameters:
        `str` - the locale String to convert, null returns null
      Returns:
        a Locale, null if null input
      Throws:
        `java.lang.IllegalArgumentException` - if the string is an invalid format
      See Also:
        `Locale.forLanguageTag(String)`

    - #### localeLookupList

          public static java.util.List<java.util.Locale> localeLookupList(java.util.Locale locale)

      Obtains the list of locales to search through when performing a locale search.

           localeLookupList(Locale("fr","CA","xxx"))
             = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr")]

      Parameters:
        `locale` - the locale to start from
      Returns:
        the unmodifiable list of Locale objects, 0 being locale, not null

    - #### localeLookupList

          public static java.util.List<java.util.Locale> localeLookupList(java.util.Locale locale,
                                                          java.util.Locale defaultLocale)

      Obtains the list of locales to search through when performing a locale search.

           localeLookupList(Locale("fr", "CA", "xxx"), Locale("en"))
             = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr"), Locale("en"]

      The result list begins with the most specific locale, then the next more general and so on, finishing with the default locale. The list will never contain the same locale twice.

      Parameters:
        `locale` - the locale to start from, null returns empty list
        `defaultLocale` - the default locale to use if no other is found
      Returns:
        the unmodifiable list of Locale objects, 0 being locale, not null

    - #### availableLocaleList

          public static java.util.List<java.util.Locale> availableLocaleList()

      Obtains an unmodifiable list of installed locales.

      This method is a wrapper around `Locale.getAvailableLocales()`. It is more efficient, as the JDK method must create a new array each time it is called.

      Returns:
        the unmodifiable list of available locales

    - #### availableLocaleSet

          public static java.util.Set<java.util.Locale> availableLocaleSet()

      Obtains an unmodifiable set of installed locales.

      This method is a wrapper around `Locale.getAvailableLocales()`. It is more efficient, as the JDK method must create a new array each time it is called.

      Returns:
        the unmodifiable set of available locales

    - #### isAvailableLocale

          public static boolean isAvailableLocale(java.util.Locale locale)

      Checks if the locale specified is in the list of available locales.

      Parameters:
        `locale` - the Locale object to check if it is available
      Returns:
        true if the locale is a known locale

    - #### languagesByCountry

          public static java.util.List<java.util.Locale> languagesByCountry(java.lang.String countryCode)

      Obtains the list of languages supported for a given country.

      This method takes a country code and searches to find the languages available for that country. Variant locales are removed.

      Parameters:
        `countryCode` - the 2 letter country code, null returns empty
      Returns:
        an unmodifiable List of Locale objects, not null

    - #### countriesByLanguage

          public static java.util.List<java.util.Locale> countriesByLanguage(java.lang.String languageCode)

      Obtains the list of countries supported for a given language.

      This method takes a language code and searches to find the countries available for that language. Variant locales are removed.

      Parameters:
        `languageCode` - the 2 letter language code, null returns empty
      Returns:
        an unmodifiable List of Locale objects, not null