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1 /* |
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2 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 package java.util.spi; |
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27 |
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28 import java.util.Locale; |
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29 |
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30 /** |
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31 * <p> |
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32 * This is the super class of all the locale sensitive service provider |
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33 * interfaces (SPIs). |
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34 * <p> |
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35 * Locale sensitive service provider interfaces are interfaces that |
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36 * correspond to locale sensitive classes in the <code>java.text</code> |
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37 * and <code>java.util</code> packages. The interfaces enable the |
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38 * construction of locale sensitive objects and the retrieval of |
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39 * localized names for these packages. Locale sensitive factory methods |
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40 * and methods for name retrieval in the <code>java.text</code> and |
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41 * <code>java.util</code> packages use implementations of the provider |
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42 * interfaces to offer support for locales beyond the set of locales |
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43 * supported by the Java runtime environment itself. |
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44 * |
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45 * <h3>Packaging of Locale Sensitive Service Provider Implementations</h3> |
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46 * Implementations of these locale sensitive services are packaged using the |
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47 * <a href="../../../../technotes/guides/extensions/index.html">Java Extension Mechanism</a> |
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48 * as installed extensions. A provider identifies itself with a |
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49 * provider-configuration file in the resource directory META-INF/services, |
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50 * using the fully qualified provider interface class name as the file name. |
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51 * The file should contain a list of fully-qualified concrete provider class names, |
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52 * one per line. A line is terminated by any one of a line feed ('\n'), a carriage |
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53 * return ('\r'), or a carriage return followed immediately by a line feed. Space |
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54 * and tab characters surrounding each name, as well as blank lines, are ignored. |
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55 * The comment character is '#' ('\u0023'); on each line all characters following |
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56 * the first comment character are ignored. The file must be encoded in UTF-8. |
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57 * <p> |
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58 * If a particular concrete provider class is named in more than one configuration |
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59 * file, or is named in the same configuration file more than once, then the |
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60 * duplicates will be ignored. The configuration file naming a particular provider |
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61 * need not be in the same jar file or other distribution unit as the provider itself. |
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62 * The provider must be accessible from the same class loader that was initially |
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63 * queried to locate the configuration file; this is not necessarily the class loader |
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64 * that loaded the file. |
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65 * <p> |
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66 * For example, an implementation of the |
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67 * {@link java.text.spi.DateFormatProvider DateFormatProvider} class should |
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68 * take the form of a jar file which contains the file: |
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69 * <pre> |
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70 * META-INF/services/java.text.spi.DateFormatProvider |
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71 * </pre> |
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72 * And the file <code>java.text.spi.DateFormatProvider</code> should have |
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73 * a line such as: |
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74 * <pre> |
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75 * <code>com.foo.DateFormatProviderImpl</code> |
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76 * </pre> |
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77 * which is the fully qualified class name of the class implementing |
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78 * <code>DateFormatProvider</code>. |
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79 * <h4>Invocation of Locale Sensitive Services</h4> |
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80 * <p> |
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81 * Locale sensitive factory methods and methods for name retrieval in the |
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82 * <code>java.text</code> and <code>java.util</code> packages invoke |
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83 * service provider methods when needed to support the requested locale. |
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84 * The methods first check whether the Java runtime environment itself |
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85 * supports the requested locale, and use its support if available. |
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86 * Otherwise, they call the {@link #isSupportedLocale(Locale) isSupportedLocale} |
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87 * methods of installed providers for the appropriate interface to find one that |
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88 * supports the requested locale. If such a provider is found, its other |
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89 * methods are called to obtain the requested object or name. When checking |
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90 * whether a locale is supported, the <a href="../Locale.html#def_extensions"> |
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91 * locale's extensions</a> are ignored by default. (If locale's extensions should |
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92 * also be checked, the {@code isSupportedLocale} method must be overridden.) |
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93 * If neither the Java runtime environment itself nor an installed provider |
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94 * supports the requested locale, the methods go through a list of candidate |
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95 * locales and repeat the availability check for each until a match is found. |
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96 * The algorithm used for creating a list of candidate locales is same as |
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97 * the one used by <code>ResourceBundle</code> by default (see |
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98 * {@link java.util.ResourceBundle.Control#getCandidateLocales getCandidateLocales} |
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99 * for the details). Even if a locale is resolved from the candidate list, |
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100 * methods that return requested objects or names are invoked with the original |
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101 * requested locale including {@code Locale} extensions. The Java runtime |
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102 * environment must support the root locale for all locale sensitive services in |
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103 * order to guarantee that this process terminates. |
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104 * <p> |
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105 * Providers of names (but not providers of other objects) are allowed to |
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106 * return null for some name requests even for locales that they claim to |
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107 * support by including them in their return value for |
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108 * <code>getAvailableLocales</code>. Similarly, the Java runtime |
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109 * environment itself may not have all names for all locales that it |
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110 * supports. This is because the sets of objects for which names are |
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111 * requested can be large and vary over time, so that it's not always |
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112 * feasible to cover them completely. If the Java runtime environment or a |
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113 * provider returns null instead of a name, the lookup will proceed as |
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114 * described above as if the locale was not supported. |
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115 * <p> |
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116 * Starting from JDK8, the search order of locale sensitive services can |
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117 * be configured by using the "java.locale.providers" system property. |
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118 * This system property declares the user's preferred order for looking up |
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119 * the locale sensitive services separated by a comma. It is only read at |
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120 * the Java runtime startup, so the later call to System.setProperty() won't |
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121 * affect the order. |
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122 * <p> |
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123 * For example, if the following is specified in the property: |
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124 * <pre> |
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125 * java.locale.providers=SPI,JRE |
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126 * </pre> |
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127 * where "SPI" represents the locale sensitive services implemented in the |
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128 * installed SPI providers, and "JRE" represents the locale sensitive services |
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129 * in the Java Runtime Environment, the locale sensitive services in the SPI |
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130 * providers are looked up first. |
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131 * <p> |
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132 * There are two other possible locale sensitive service providers, i.e., "CLDR" |
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133 * which is a provider based on Unicode Consortium's |
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134 * <a href="http://cldr.unicode.org/">CLDR Project</a>, and "HOST" which is a |
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135 * provider that reflects the user's custom settings in the underlying operating |
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136 * system. These two providers may not be available, depending on the Java Runtime |
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137 * Environment implementation. Specifying "JRE,SPI" is identical to the default |
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138 * behavior, which is compatibile with the prior releases. |
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139 * |
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140 * @since 1.6 |
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141 */ |
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142 public abstract class LocaleServiceProvider { |
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143 |
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144 /** |
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145 * Sole constructor. (For invocation by subclass constructors, typically |
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146 * implicit.) |
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147 */ |
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148 protected LocaleServiceProvider() { |
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149 } |
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150 |
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151 /** |
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152 * Returns an array of all locales for which this locale service provider |
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153 * can provide localized objects or names. This information is used to |
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154 * compose {@code getAvailableLocales()} values of the locale-dependent |
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155 * services, such as {@code DateFormat.getAvailableLocales()}. |
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156 * |
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157 * <p>The array returned by this method should not include two or more |
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158 * {@code Locale} objects only differing in their extensions. |
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159 * |
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160 * @return An array of all locales for which this locale service provider |
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161 * can provide localized objects or names. |
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162 */ |
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163 public abstract Locale[] getAvailableLocales(); |
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164 |
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165 /** |
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166 * Returns {@code true} if the given {@code locale} is supported by |
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167 * this locale service provider. The given {@code locale} may contain |
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168 * <a href="../Locale.html#def_extensions">extensions</a> that should be |
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169 * taken into account for the support determination. |
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170 * |
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171 * <p>The default implementation returns {@code true} if the given {@code locale} |
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172 * is equal to any of the available {@code Locale}s returned by |
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173 * {@link #getAvailableLocales()} with ignoring any extensions in both the |
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174 * given {@code locale} and the available locales. Concrete locale service |
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175 * provider implementations should override this method if those |
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176 * implementations are {@code Locale} extensions-aware. For example, |
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177 * {@code DecimalFormatSymbolsProvider} implementations will need to check |
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178 * extensions in the given {@code locale} to see if any numbering system is |
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179 * specified and can be supported. However, {@code CollatorProvider} |
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180 * implementations may not be affected by any particular numbering systems, |
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181 * and in that case, extensions for numbering systems should be ignored. |
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182 * |
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183 * @param locale a {@code Locale} to be tested |
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184 * @return {@code true} if the given {@code locale} is supported by this |
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185 * provider; {@code false} otherwise. |
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186 * @throws NullPointerException |
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187 * if the given {@code locale} is {@code null} |
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188 * @see Locale#hasExtensions() |
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189 * @see Locale#stripExtensions() |
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190 * @since 1.8 |
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191 */ |
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192 public boolean isSupportedLocale(Locale locale) { |
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193 locale = locale.stripExtensions(); // throws NPE if locale == null |
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194 for (Locale available : getAvailableLocales()) { |
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195 if (locale.equals(available.stripExtensions())) { |
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196 return true; |
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197 } |
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198 } |
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199 return false; |
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200 } |
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201 } |