The LocaleServiceProvider.java Java example source code
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package java.util.spi;
import java.util.Locale;
/**
* <p>
* This is the super class of all the locale sensitive service provider
* interfaces (SPIs).
* <p>
* Locale sensitive service provider interfaces are interfaces that
* correspond to locale sensitive classes in the <code>java.text
* and <code>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 <code>java.text and
* <code>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.
*
* <h3>Packaging of Locale Sensitive Service Provider Implementations
* Implementations of these locale sensitive services are packaged using the
* <a href="../../../../technotes/guides/extensions/index.html">Java Extension Mechanism
* as installed extensions. A provider identifies itself with a
* provider-configuration file in the resource directory META-INF/services,
* using the fully qualified provider interface class name as the file name.
* The file should contain a list of fully-qualified concrete provider class names,
* one per line. A line is terminated by any one of a line feed ('\n'), a carriage
* return ('\r'), or a carriage return followed immediately by a line feed. Space
* and tab characters surrounding each name, as well as blank lines, are ignored.
* The comment character is '#' ('\u0023'); on each line all characters following
* the first comment character are ignored. The file must be encoded in UTF-8.
* <p>
* 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.
* <p>
* 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:
* <pre>
* META-INF/services/java.text.spi.DateFormatProvider
* </pre>
* And the file <code>java.text.spi.DateFormatProvider should have
* a line such as:
* <pre>
* <code>com.foo.DateFormatProviderImpl
* </pre>
* which is the fully qualified class name of the class implementing
* <code>DateFormatProvider.
* <h4>Invocation of Locale Sensitive Services
* <p>
* Locale sensitive factory methods and methods for name retrieval in the
* <code>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 <a href="../Locale.html#def_extensions">
* locale's extensions</a> 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 <code>ResourceBundle 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.
* <p>
* 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
* <code>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.
* <p>
* 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.
* <p>
* For example, if the following is specified in the property:
* <pre>
* java.locale.providers=SPI,JRE
* </pre>
* 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.
* <p>
* There are two other possible locale sensitive service providers, i.e., "CLDR"
* which is a provider based on Unicode Consortium's
* <a href="http://cldr.unicode.org/">CLDR Project, and "HOST" which is a
* provider that reflects the user's custom settings in the underlying operating
* system. These two providers may not be available, depending on the Java Runtime
* Environment implementation. Specifying "JRE,SPI" is identical to the default
* behavior, which is compatibile with the prior releases.
*
* @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()}.
*
* <p>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
* <a href="../Locale.html#def_extensions">extensions that should be
* taken into account for the support determination.
*
* <p>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;
}
}
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