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279 lines
14 KiB
Java
279 lines
14 KiB
Java
/*
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* Copyright (c) 2005, 2024, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util.spi;
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import java.util.Locale;
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/**
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* <p>
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* This is the super class of all the locale sensitive service provider
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* interfaces (SPIs).
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* <p>
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* Locale sensitive service provider interfaces are interfaces that
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* correspond to locale sensitive classes in the {@code java.text}
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* and {@code java.util} packages in order to provide the locale
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* data used for each service. The interfaces enable the
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* construction of locale sensitive objects and the retrieval of
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* localized names for these packages. Locale sensitive factory methods
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* and methods for name retrieval in the {@code java.text} and
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* {@code java.util} packages use implementations of the provider
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* interfaces to offer support for locales beyond the set of locales
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* supported by the Java runtime environment itself. Locale sensitive service
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* providers are deployed on the application module path or the application class
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* path. In order to be looked up, providers must be visible to the {@link
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* ClassLoader#getSystemClassLoader() system class loader}.
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* See {@link java.util.ServiceLoader##developing-service-providers Deploying
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* Service Providers} for further detail on deploying a locale sensitive service
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* provider as a module or on the class path.
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*
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* <h2>Packaging of Locale Sensitive Service Provider Implementations</h2>
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*
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* <p> For a locale sensitive service provider deployed in a module, the <i>provides</i>
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* directive must be specified in the module declaration. The <i>provides</i>
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* directive specifies both the service and the service provider.
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*
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* <p> For example, an implementation of the {@link java.text.spi.DateFormatProvider
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* DateFormatProvider} class deployed as a module might specify the following directive:
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* <pre>{@code
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* provides java.text.spi.DateFormatProvider with com.example.ExternalDateFormatProvider;
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* }</pre>
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*
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* <p> For a Locale Service Provider deployed on the class path, the provider
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* identifies itself with a provider-configuration file in the resource directory
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* META-INF/services. The file name should be the fully fully qualified provider
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* interface class name. The file should contain a list of fully-qualified concrete
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* provider class names, one per line. A line is terminated by any one of a line
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* feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately
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* by a line feed. Space and tab characters surrounding each name, as well as
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* blank lines, are ignored. The comment character is '#' ('\u0023'); on each line
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* all characters following the first comment character are ignored. The file must
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* be encoded in UTF-8.
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* <p>
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* If a particular concrete provider class is named in more than one configuration
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* file, or is named in the same configuration file more than once, then the
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* duplicates will be ignored. The configuration file naming a particular provider
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* need not be in the same jar file or other distribution unit as the provider itself.
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* The provider must be accessible from the same class loader that was initially
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* queried to locate the configuration file; this is not necessarily the class loader
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* that loaded the file.
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* <p>
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* For example, an implementation of the
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* {@link java.text.spi.DateFormatProvider DateFormatProvider} class should
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* take the form of a jar file which contains the file:
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* <pre>
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* META-INF/services/java.text.spi.DateFormatProvider
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* </pre>
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* And the file {@code java.text.spi.DateFormatProvider} should have
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* a line such as:
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* <pre>
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* {@code com.foo.DateFormatProviderImpl}
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* </pre>
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* which is the fully qualified class name of the class implementing
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* {@code DateFormatProvider}.
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* <h2>Invocation of Locale Sensitive Services</h2>
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* <p>
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* Locale sensitive factory methods and methods for name retrieval in the
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* {@code java.text} and {@code java.util} packages invoke
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* service provider methods when needed to support the requested locale.
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* The methods first check whether the Java runtime environment itself
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* supports the requested locale, and use its support if available.
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* Otherwise, they call the {@link #isSupportedLocale(Locale) isSupportedLocale}
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* methods of installed providers for the appropriate interface to find one that
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* supports the requested locale. If such a provider is found, its other
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* methods are called to obtain the requested object or name. When checking
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* whether a locale is supported, the {@linkplain Locale##def_extensions
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* locale's extensions} are ignored by default. (If a locale's extensions should
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* also be checked, the {@code isSupportedLocale} method must be overridden).
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* If neither the Java runtime environment itself nor an installed provider
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* supports the requested locale, the methods go through a list of candidate
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* locales and repeat the availability check for each until a match is found.
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* The algorithm used for creating a list of candidate locales is same as
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* the one used by {@code ResourceBundle} by default (see
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* {@link java.util.ResourceBundle.Control#getCandidateLocales getCandidateLocales}
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* for the details). Even if a locale is resolved from the candidate list,
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* methods that return requested objects or names are invoked with the original
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* requested locale including {@code Locale} extensions. The Java runtime
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* environment must support the root locale for all locale sensitive services in
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* order to guarantee that this process terminates.
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* <p>
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* Providers of names (but not providers of other objects) are allowed to
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* return null for some name requests even for locales that they claim to
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* support by including them in their return value for
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* {@code getAvailableLocales}. Similarly, the Java runtime
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* environment itself may not have all names for all locales that it
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* supports. This is because the sets of objects for which names are
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* requested can be large and vary over time, so that it's not always
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* feasible to cover them completely. If the Java runtime environment or a
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* provider returns null instead of a name, the lookup will proceed as
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* described above as if the locale was not supported.
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* <p>
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* The search order of locale sensitive services can
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* be configured by using the {@systemProperty java.locale.providers} system property.
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* This system property declares the user's preferred order for looking up
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* the locale sensitive services separated by a comma. As this property value is
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* read and cached only at the initialization of this class, users should specify the
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* property on the java launcher command line. Setting it at runtime with
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* {@link System#setProperty(String, String)} is discouraged and it may not affect
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* the order.
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* JDK Reference Implementation provides the following three
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* locale data providers:
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* <ul>
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* <li> "CLDR": A locale data provider based on the Unicode Consortium's
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* <a href="http://cldr.unicode.org/">Common Locale Data Repository (CLDR)</a>.
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* <li> "SPI": represents the locale sensitive services implementing the subclasses of
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* this {@code LocaleServiceProvider} class.
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* <li> "HOST": A locale data provider that reflects the user's custom settings in the
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* underlying operating system. This provider may not be available, depending
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* on the JDK Reference Implementation.
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* </ul>
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* <p>
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* For example, if the following is specified in the property:
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* <pre>
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* java.locale.providers=SPI,CLDR
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* </pre>
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* the locale sensitive services in the SPI providers are looked up first. If the
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* desired locale sensitive service is not available, then the runtime looks for CLDR.
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* <p>
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* The default value for looking up the preferred locale data providers is "CLDR",
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* so specifying only "CLDR" is identical to the default behavior. Applications which
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* require implementations of the locale sensitive services must explicitly specify
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* "SPI" in order for the Java runtime to load them from the classpath.
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*
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* @implNote The JDK uses locale data from the Unicode Consortium's
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* <a href="http://cldr.unicode.org/">Common Locale Data Repository (CLDR)</a>
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* to implement locale-sensitive APIs in the {@code java.util} and
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* {@code java.text} packages. This locale data derives the set of locales
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* supported by the Java runtime environment. The following table lists the
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* version of CLDR used in each JDK release. Unless otherwise specified, all
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* update releases in a given JDK release family use the same CLDR version.
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* Note that the CLDR locale data are subject to change. Users should not assume
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* that the locale data remain the same across CLDR versions. Otherwise, unexpected
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* incompatible behaviors may occur, such as an exception on parsing a date.
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* Refer to <a href="https://cldr.unicode.org/index/downloads">CLDR Releases</a>
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* for the deltas between their releases.
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* <table class="striped">
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* <caption style="display:none">JDK releases and supported CLDR versions</caption>
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* <thead>
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* <tr><th scope="col">JDK release</th>
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* <th scope="col">CLDR version</th></tr>
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* </thead>
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* <tbody>
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* <tr><th scope="row" style="text-align:left">JDK 24</th>
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* <td>CLDR 46</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 23</th>
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* <td>CLDR 45</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 22</th>
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* <td>CLDR 44</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 21</th>
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* <td>CLDR 43</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 20</th>
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* <td>CLDR 42</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 19</th>
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* <td>CLDR 41</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 18</th>
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* <td>CLDR 39</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 17</th>
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* <td>CLDR 39</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 16</th>
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* <td>CLDR 38</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 15</th>
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* <td>CLDR 37</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 14</th>
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* <td>CLDR 36</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 13</th>
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* <td>CLDR 35.1</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 12</th>
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* <td>CLDR 33</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 11</th>
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* <td>CLDR 33</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 10</th>
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* <td>CLDR 29</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 9</th>
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* <td>CLDR 29</td></tr>
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* <tr><th scope="row" style="text-align:left">JDK 8</th>
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* <td>CLDR 21.0.1</td></tr>
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* </tbody>
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* </table>
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*
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* @since 1.6
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*/
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public abstract class LocaleServiceProvider {
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/**
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* Initializes a new locale service provider.
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*/
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protected LocaleServiceProvider() {}
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/**
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* {@return an array of all locales for which this locale service provider
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* can provide localized objects or names}
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*
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* This information is used to compose {@code getAvailableLocales()}
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* values of the locale-dependent services, such as
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* {@code DateFormat.getAvailableLocales()}.
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*
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* <p>The array returned by this method should not include two or more
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* {@code Locale} objects only differing in their extensions.
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*/
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public abstract Locale[] getAvailableLocales();
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/**
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* Returns {@code true} if the given {@code locale} is supported by
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* this locale service provider. The given {@code locale} may contain
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* {@linkplain Locale##def_extensions extensions} that should be
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* taken into account for the support determination.
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*
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* <p>The default implementation returns {@code true} if the given {@code locale}
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* is equal to any of the available {@code Locale}s returned by
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* {@link #getAvailableLocales()} with ignoring any extensions in both the
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* given {@code locale} and the available locales. Concrete locale service
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* provider implementations should override this method if those
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* implementations are {@code Locale} extensions-aware. For example,
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* {@code DecimalFormatSymbolsProvider} implementations will need to check
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* extensions in the given {@code locale} to see if any numbering system is
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* specified and can be supported. However, {@code CollatorProvider}
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* implementations may not be affected by any particular numbering systems,
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* and in that case, extensions for numbering systems should be ignored.
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*
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* @param locale a {@code Locale} to be tested
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* @return {@code true} if the given {@code locale} is supported by this
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* provider; {@code false} otherwise.
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* @throws NullPointerException
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* if the given {@code locale} is {@code null}
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* @see Locale#hasExtensions()
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* @see Locale#stripExtensions()
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* @since 1.8
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*/
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public boolean isSupportedLocale(Locale locale) {
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locale = locale.stripExtensions(); // throws NPE if locale == null
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for (Locale available : getAvailableLocales()) {
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if (locale.equals(available.stripExtensions())) {
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return true;
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}
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}
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return false;
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}
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}
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