Class LocaleServiceProvider

This is the superclass of all the {@link Locale} service provider interfaces or SPIs. The locale SPIs are used to allow for the provision of additional support for locale-specific data. The runtime environment has its own collection of locale data, but these interfaces allow this to be extended by external classes.

Service providers are created as concrete implementations of these interfaces, and accessed using the extension mechanism, realised by {@link ServiceLoader}. When a factory method of one of the locale-specific classes (such as {@link java.text.DateFormatSymbols} or {@link java.util.Currency}) is called, the runtime environment is first asked to provide data for the specified locale. If the runtime environment fails to provide this, then the offer is made to service providers which implement the appropriate interface.

Each provider implements the method specified by this class, {@link #getAvailableLocales()}. This method is called first to determine whether the provider will be of any use in providing data for the specified locale. If a provider is found to be capable, then a more specific method appropriate to the class requiring the data will be called. In the case of {@link java.text.DateFormatSymbols}, this would be {@link java.text.spi.DateFormatSymbols#getInstance(Locale)}.

If neither a service provider nor the runtime environment itself can fulfill the request, a fallback procedure is engaged. The locale is modified by applying the first applicable rule:

1. If the variant contains a '_', then this and everything following it is trimmed.
2. If the variant is non-empty, it is converted to an empty string.
3. If the country is non-empty, it is converted to an empty string.
4. If the language is non-empty, it is converted to an empty string.

The modified locale is then used to start the same process again. The root locale (@link java.util.Locale#ROOT} must be supported by the runtime environment in order to terminate this cycle.

Note that any names returned by the providers may be null. Returning a null name is considered equivalent to not supporting a particular locale.

Since: 1.6