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202 lines
9.3 KiB
202 lines
9.3 KiB
/*
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* Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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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</code>
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* and <code>java.util</code> packages. 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</code> and
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* <code>java.util</code> 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.
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*
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* <h3>Packaging of Locale Sensitive Service Provider Implementations</h3>
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* Implementations of these locale sensitive services are packaged using the
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* <a href="../../../../technotes/guides/extensions/index.html">Java Extension Mechanism</a>
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* as installed extensions. A provider identifies itself with a
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* provider-configuration file in the resource directory META-INF/services,
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* using the fully qualified provider interface class name as the file name.
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* The file should contain a list of fully-qualified concrete provider class names,
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* one per line. A line is terminated by any one of a line feed ('\n'), a carriage
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* return ('\r'), or a carriage return followed immediately by a line feed. Space
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* and tab characters surrounding each name, as well as blank lines, are ignored.
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* The comment character is '#' ('\u0023'); on each line all characters following
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* the first comment character are ignored. The file must 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</code> should have
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* a line such as:
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* <pre>
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* <code>com.foo.DateFormatProviderImpl</code>
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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</code>.
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* <h4>Invocation of Locale Sensitive Services</h4>
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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</code> and <code>java.util</code> 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 <a href="../Locale.html#def_extensions">
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* locale's extensions</a> are ignored by default. (If 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</code> 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</code>. 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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* Starting from JDK8, the search order of locale sensitive services can
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* be configured by using the "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. It is only read at
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* the Java runtime startup, so the later call to System.setProperty() won't
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* affect the order.
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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,JRE
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* </pre>
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* where "SPI" represents the locale sensitive services implemented in the
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* installed SPI providers, and "JRE" represents the locale sensitive services
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* in the Java Runtime Environment, the locale sensitive services in the SPI
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* providers are looked up first.
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* <p>
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* There are two other possible locale sensitive service providers, i.e., "CLDR"
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* which is a provider based on Unicode Consortium's
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* <a href="http://cldr.unicode.org/">CLDR Project</a>, and "HOST" which is a
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* provider that reflects the user's custom settings in the underlying operating
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* system. These two providers may not be available, depending on the Java Runtime
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* Environment implementation. Specifying "JRE,SPI" is identical to the default
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* behavior, which is compatibile with the prior releases.
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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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* Sole constructor. (For invocation by subclass constructors, typically
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* implicit.)
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*/
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protected LocaleServiceProvider() {
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}
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/**
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* Returns an array of all locales for which this locale service provider
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* can provide localized objects or names. This information is used to
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* compose {@code getAvailableLocales()} values of the locale-dependent
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* services, such as {@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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* @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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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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* <a href="../Locale.html#def_extensions">extensions</a> 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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