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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</code>

 * and <code>java.util</code> 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</code> and

 * <code>java.util</code> 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</h3>

 * Implementations of these locale sensitive services are packaged using the

 * <a href="../../../../technotes/guides/extensions/index.html">Java Extension Mechanism</a>

 * 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</code> should have

 * a line such as:

 * <pre>

 * <code>com.foo.DateFormatProviderImpl</code>

 * </pre>

 * which is the fully qualified class name of the class implementing

 * <code>DateFormatProvider</code>.

 * <h4>Invocation of Locale Sensitive Services</h4>

 * <p>

 * Locale sensitive factory methods and methods for name retrieval in the

 * <code>java.text</code> and <code>java.util</code> 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</code> 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</code>. 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</a>, 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</a> 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;

    }

}