* This is the super class of all the locale sensitive service provider * interfaces (SPIs). *
* Locale sensitive service provider interfaces are interfaces that
* correspond to locale sensitive classes in the java.text
* and java.util packages. The interfaces enable the
* construction of locale sensitive objects and the retrieval of
* localized names for these packages. Locale sensitive factory methods
* and methods for name retrieval in the java.text and
* java.util packages use implementations of the provider
* interfaces to offer support for locales beyond the set of locales
* supported by the Java runtime environment itself.
*
*
* If a particular concrete provider class is named in more than one configuration * file, or is named in the same configuration file more than once, then the * duplicates will be ignored. The configuration file naming a particular provider * need not be in the same jar file or other distribution unit as the provider itself. * The provider must be accessible from the same class loader that was initially * queried to locate the configuration file; this is not necessarily the class loader * that loaded the file. *
* For example, an implementation of the * {@link java.text.spi.DateFormatProvider DateFormatProvider} class should * take the form of a jar file which contains the file: *
* META-INF/services/java.text.spi.DateFormatProvider ** And the file
java.text.spi.DateFormatProvider should have
* a line such as:
*
* com.foo.DateFormatProviderImpl
*
* which is the fully qualified class name of the class implementing
* DateFormatProvider.
*
* Locale sensitive factory methods and methods for name retrieval in the
* java.text and java.util packages invoke
* service provider methods when needed to support the requested locale.
* The methods first check whether the Java runtime environment itself
* supports the requested locale, and use its support if available.
* Otherwise, they call the {@link #isSupportedLocale(Locale) isSupportedLocale}
* methods of installed providers for the appropriate interface to find one that
* supports the requested locale. If such a provider is found, its other
* methods are called to obtain the requested object or name. When checking
* whether a locale is supported, the
* locale's extensions are ignored by default. (If locale's extensions should
* also be checked, the {@code isSupportedLocale} method must be overridden.)
* If neither the Java runtime environment itself nor an installed provider
* supports the requested locale, the methods go through a list of candidate
* locales and repeat the availability check for each until a match is found.
* The algorithm used for creating a list of candidate locales is same as
* the one used by ResourceBunlde by default (see
* {@link java.util.ResourceBundle.Control#getCandidateLocales getCandidateLocales}
* for the details). Even if a locale is resolved from the candidate list,
* methods that return requested objects or names are invoked with the original
* requested locale including {@code Locale} extensions. The Java runtime
* environment must support the root locale for all locale sensitive services in
* order to guarantee that this process terminates.
*
* Providers of names (but not providers of other objects) are allowed to
* return null for some name requests even for locales that they claim to
* support by including them in their return value for
* getAvailableLocales. Similarly, the Java runtime
* environment itself may not have all names for all locales that it
* supports. This is because the sets of objects for which names are
* requested can be large and vary over time, so that it's not always
* feasible to cover them completely. If the Java runtime environment or a
* provider returns null instead of a name, the lookup will proceed as
* described above as if the locale was not supported.
*
* Starting from JDK8, the search order of locale sensitive services can * be configured by using the "java.locale.providers" system property. * This system property declares the user's preferred order for looking up * the locale sensitive services separated by a comma. It is only read at * the Java runtime startup, so the later call to System.setProperty() won't * affect the order. *
* For example, if the following is specified in the property: *
* java.locale.providers=SPI,JRE ** where "SPI" represents the locale sensitive services implemented in the * installed SPI providers, and "JRE" represents the locale sensitive services * in the Java Runtime Environment, the locale sensitive services in the SPI * providers are looked up first. * * @since 1.6 */ public abstract class LocaleServiceProvider { /** * Sole constructor. (For invocation by subclass constructors, typically * implicit.) */ protected LocaleServiceProvider() { } /** * Returns an array of all locales for which this locale service provider * can provide localized objects or names. This information is used to * compose {@code getAvailableLocales()} values of the locale-dependent * services, such as {@code DateFormat.getAvailableLocales()}. * *
The array returned by this method should not include two or more * {@code Locale} objects only differing in their extensions. * * @return An array of all locales for which this locale service provider * can provide localized objects or names. */ public abstract Locale[] getAvailableLocales(); /** * Returns {@code true} if the given {@code locale} is supported by * this locale service provider. The given {@code locale} may contain * extensions that should be * taken into account for the support determination. * *
The default implementation returns {@code true} if the given {@code locale} * is equal to any of the available {@code Locale}s returned by * {@link #getAvailableLocales()} with ignoring any extensions in both the * given {@code locale} and the available locales. Concrete locale service * provider implementations should override this method if those * implementations are {@code Locale} extensions-aware. For example, * {@code DecimalFormatSymbolsProvider} implementations will need to check * extensions in the given {@code locale} to see if any numbering system is * specified and can be supported. However, {@code CollatorProvider} * implementations may not be affected by any particular numbering systems, * and in that case, extensions for numbering systems should be ignored. * * @param locale a {@code Locale} to be tested * @return {@code true} if the given {@code locale} is supported by this * provider; {@code false} otherwise. * @throws NullPointerException * if the given {@code locale} is {@code null} * @see Locale#hasExtensions() * @see Locale#stripExtensions() * @since 1.8 */ public boolean isSupportedLocale(Locale locale) { locale = locale.stripExtensions(); // throws NPE if locale == null for (Locale available : getAvailableLocales()) { if (locale.equals(available.stripExtensions())) { return true; } } return false; } }