1 /*
2 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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7 * published by the Free Software Foundation. Oracle designates this
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9 * by Oracle in the LICENSE file that accompanied this code.
10 *
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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24 */
25
26 package java.util.spi;
27
28 import java.util.Locale;
29
30 /**
31 * <p>
32 * This is the super class of all the locale sensitive service provider
33 * interfaces (SPIs).
34 * <p>
35 * Locale sensitive service provider interfaces are interfaces that
36 * correspond to locale sensitive classes in the <code>java.text</code>
37 * and <code>java.util</code> packages. The interfaces enable the
38 * construction of locale sensitive objects and the retrieval of
39 * localized names for these packages. Locale sensitive factory methods
40 * and methods for name retrieval in the <code>java.text</code> and
41 * <code>java.util</code> packages use implementations of the provider
42 * interfaces to offer support for locales beyond the set of locales
43 * supported by the Java runtime environment itself.
44 * <p>
45 * <h4>Packaging of Locale Sensitive Service Provider Implementations</h4>
46 * Implementations of these locale sensitive services are packaged using the
47 * <a href="../../../../technotes/guides/extensions/index.html">Java Extension Mechanism</a>
48 * as installed extensions. A provider identifies itself with a
49 * provider-configuration file in the resource directory META-INF/services,
50 * using the fully qualified provider interface class name as the file name.
51 * The file should contain a list of fully-qualified concrete provider class names,
52 * one per line. A line is terminated by any one of a line feed ('\n'), a carriage
53 * return ('\r'), or a carriage return followed immediately by a line feed. Space
54 * and tab characters surrounding each name, as well as blank lines, are ignored.
55 * The comment character is '#' ('\u0023'); on each line all characters following
56 * the first comment character are ignored. The file must be encoded in UTF-8.
57 * <p>
58 * If a particular concrete provider class is named in more than one configuration
59 * file, or is named in the same configuration file more than once, then the
60 * duplicates will be ignored. The configuration file naming a particular provider
61 * need not be in the same jar file or other distribution unit as the provider itself.
62 * The provider must be accessible from the same class loader that was initially
63 * queried to locate the configuration file; this is not necessarily the class loader
64 * that loaded the file.
65 * <p>
66 * For example, an implementation of the
67 * {@link java.text.spi.DateFormatProvider DateFormatProvider} class should
68 * take the form of a jar file which contains the file:
69 * <pre>
70 * META-INF/services/java.text.spi.DateFormatProvider
71 * </pre>
72 * And the file <code>java.text.spi.DateFormatProvider</code> should have
73 * a line such as:
74 * <pre>
75 * <code>com.foo.DateFormatProviderImpl</code>
76 * </pre>
77 * which is the fully qualified class name of the class implementing
78 * <code>DateFormatProvider</code>.
79 * <h4>Invocation of Locale Sensitive Services</h4>
80 * <p>
81 * Locale sensitive factory methods and methods for name retrieval in the
82 * <code>java.text</code> and <code>java.util</code> packages invoke
83 * service provider methods when needed to support the requested locale.
84 * The methods first check whether the Java runtime environment itself
85 * supports the requested locale, and use its support if available.
86 * Otherwise, they call the <code>getAvailableLocales()</code> methods of
87 * installed providers for the appropriate interface to find one that
88 * supports the requested locale. If such a provider is found, its other
89 * methods are called to obtain the requested object or name. When checking
90 * whether a locale is supported, the locale's extensions are ignored.
91 * If neither the Java runtime environment itself nor an installed provider
92 * supports the requested locale, the methods go through a list of candidate
93 * locales and repeat the availability check for each until a match is found.
94 * The algorithm used for creating a list of candidate locales is same as
95 * the one used by <code>ResourceBunlde</code> by default (see
96 * {@link java.util.ResourceBundle.Control#getCandidateLocales getCandidateLocales}
97 * for the details). Even if a locale is resolved from the candidate list,
98 * methods that return requested objects or names are invoked with the original
99 * requested locale including extensions. The Java runtime environment must
100 * support the root locale for all locale sensitive services in order to
101 * guarantee that this process terminates.
102 * <p>
103 * Providers of names (but not providers of other objects) are allowed to
104 * return null for some name requests even for locales that they claim to
105 * support by including them in their return value for
106 * <code>getAvailableLocales</code>. Similarly, the Java runtime
107 * environment itself may not have all names for all locales that it
108 * supports. This is because the sets of objects for which names are
109 * requested can be large and vary over time, so that it's not always
110 * feasible to cover them completely. If the Java runtime environment or a
111 * provider returns null instead of a name, the lookup will proceed as
112 * described above as if the locale was not supported.
113 *
114 * @since 1.6
115 */
116 public abstract class LocaleServiceProvider {
117
118 /**
119 * Sole constructor. (For invocation by subclass constructors, typically
120 * implicit.)
121 */
122 protected LocaleServiceProvider() {
123 }
124
125 /**
126 * Returns an array of all locales for which this locale service provider
127 * can provide localized objects or names.
128 * <p>
129 * <b>Note:</b> Extensions in a <code>Locale</code> are ignored during
130 * service provider lookup. So the array returned by this method should
131 * not include two or more <code>Locale</code> objects only differing in
132 * their extensions.
133 *
134 * @return An array of all locales for which this locale service provider
135 * can provide localized objects or names.
136 */
137 public abstract Locale[] getAvailableLocales();
138 }