Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Locale; import java.util.Map; import java.util.Set; /** * <p>Operations to assist when working with a {@link Locale}.</p> * * <p>This class tries to handle <code>null</code> input gracefully. * An exception will not be thrown for a <code>null</code> input. * Each method documents its behaviour in more detail.</p> * * @author Stephen Colebourne * @since 2.2 * @version $Id: LocaleUtils.java 534277 2007-05-01 23:50:01Z bayard $ */ public class LocaleUtils { /** Unmodifiable list of available locales. */ private static final List cAvailableLocaleList; /** Unmodifiable set of available locales. */ private static Set cAvailableLocaleSet; /** Unmodifiable map of language locales by country. */ private static final Map cLanguagesByCountry = Collections.synchronizedMap(new HashMap()); /** Unmodifiable map of country locales by language. */ private static final Map cCountriesByLanguage = Collections.synchronizedMap(new HashMap()); static { List list = Arrays.asList(Locale.getAvailableLocales()); cAvailableLocaleList = Collections.unmodifiableList(list); } /** * <p><code>LocaleUtils</code> instances should NOT be constructed in standard programming. * Instead, the class should be used as <code>LocaleUtils.toLocale("en_GB");</code>.</p> * * <p>This constructor is public to permit tools that require a JavaBean instance * to operate.</p> */ public LocaleUtils() { super(); } //----------------------------------------------------------------------- /** * <p>Converts a String to a Locale.</p> * * <p>This method takes the string format of a locale and creates the * locale object from it.</p> * * <pre> * LocaleUtils.toLocale("en") = new Locale("en", "") * LocaleUtils.toLocale("en_GB") = new Locale("en", "GB") * LocaleUtils.toLocale("en_GB_xxx") = new Locale("en", "GB", "xxx") (#) * </pre> * * <p>(#) The behaviour of the JDK variant constructor changed between JDK1.3 and JDK1.4. * In JDK1.3, the constructor upper cases the variant, in JDK1.4, it doesn't. * Thus, the result from getVariant() may vary depending on your JDK.</p> * * <p>This method validates the input strictly. * The language code must be lowercase. * The country code must be uppercase. * The separator must be an underscore. * The length must be correct. * </p> * * @param str the locale String to convert, null returns null * @return a Locale, null if null input * @throws IllegalArgumentException if the string is an invalid format */ public static Locale toLocale(String str) { if (str == null) { return null; } int len = str.length(); if (len != 2 && len != 5 && len < 7) { throw new IllegalArgumentException("Invalid locale format: " + str); } char ch0 = str.charAt(0); char ch1 = str.charAt(1); if (ch0 < 'a' || ch0 > 'z' || ch1 < 'a' || ch1 > 'z') { throw new IllegalArgumentException("Invalid locale format: " + str); } if (len == 2) { return new Locale(str, ""); } else { if (str.charAt(2) != '_') { throw new IllegalArgumentException("Invalid locale format: " + str); } char ch3 = str.charAt(3); if (ch3 == '_') { return new Locale(str.substring(0, 2), "", str.substring(4)); } char ch4 = str.charAt(4); if (ch3 < 'A' || ch3 > 'Z' || ch4 < 'A' || ch4 > 'Z') { throw new IllegalArgumentException("Invalid locale format: " + str); } if (len == 5) { return new Locale(str.substring(0, 2), str.substring(3, 5)); } else { if (str.charAt(5) != '_') { throw new IllegalArgumentException("Invalid locale format: " + str); } return new Locale(str.substring(0, 2), str.substring(3, 5), str.substring(6)); } } } //----------------------------------------------------------------------- /** * <p>Obtains the list of locales to search through when performing * a locale search.</p> * * <pre> * localeLookupList(Locale("fr","CA","xxx")) * = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr")] * </pre> * * @param locale the locale to start from * @return the unmodifiable list of Locale objects, 0 being locale, never null */ public static List localeLookupList(Locale locale) { return localeLookupList(locale, locale); } //----------------------------------------------------------------------- /** * <p>Obtains the list of locales to search through when performing * a locale search.</p> * * <pre> * localeLookupList(Locale("fr", "CA", "xxx"), Locale("en")) * = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr"), Locale("en"] * </pre> * * <p>The result list begins with the most specific locale, then the * next more general and so on, finishing with the default locale. * The list will never contain the same locale twice.</p> * * @param locale the locale to start from, null returns empty list * @param defaultLocale the default locale to use if no other is found * @return the unmodifiable list of Locale objects, 0 being locale, never null */ public static List localeLookupList(Locale locale, Locale defaultLocale) { List list = new ArrayList(4); if (locale != null) { list.add(locale); if (locale.getVariant().length() > 0) { list.add(new Locale(locale.getLanguage(), locale.getCountry())); } if (locale.getCountry().length() > 0) { list.add(new Locale(locale.getLanguage(), "")); } if (list.contains(defaultLocale) == false) { list.add(defaultLocale); } } return Collections.unmodifiableList(list); } //----------------------------------------------------------------------- /** * <p>Obtains an unmodifiable list of installed locales.</p> * * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}. * It is more efficient, as the JDK method must create a new array each * time it is called.</p> * * @return the unmodifiable list of available locales */ public static List availableLocaleList() { return cAvailableLocaleList; } //----------------------------------------------------------------------- /** * <p>Obtains an unmodifiable set of installed locales.</p> * * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}. * It is more efficient, as the JDK method must create a new array each * time it is called.</p> * * @return the unmodifiable set of available locales */ public static Set availableLocaleSet() { Set set = cAvailableLocaleSet; if (set == null) { set = new HashSet(availableLocaleList()); set = Collections.unmodifiableSet(set); cAvailableLocaleSet = set; } return set; } //----------------------------------------------------------------------- /** * <p>Checks if the locale specified is in the list of available locales.</p> * * @param locale the Locale object to check if it is available * @return true if the locale is a known locale */ public static boolean isAvailableLocale(Locale locale) { return availableLocaleList().contains(locale); } //----------------------------------------------------------------------- /** * <p>Obtains the list of languages supported for a given country.</p> * * <p>This method takes a country code and searches to find the * languages available for that country. Variant locales are removed.</p> * * @param countryCode the 2 letter country code, null returns empty * @return an unmodifiable List of Locale objects, never null */ public static List languagesByCountry(String countryCode) { List langs = (List) cLanguagesByCountry.get(countryCode); //syncd if (langs == null) { if (countryCode != null) { langs = new ArrayList(); List locales = availableLocaleList(); for (int i = 0; i < locales.size(); i++) { Locale locale = (Locale) locales.get(i); if (countryCode.equals(locale.getCountry()) && locale.getVariant().length() == 0) { langs.add(locale); } } langs = Collections.unmodifiableList(langs); } else { langs = Collections.EMPTY_LIST; } cLanguagesByCountry.put(countryCode, langs); //syncd } return langs; } //----------------------------------------------------------------------- /** * <p>Obtains the list of countries supported for a given language.</p> * * <p>This method takes a language code and searches to find the * countries available for that language. Variant locales are removed.</p> * * @param languageCode the 2 letter language code, null returns empty * @return an unmodifiable List of Locale objects, never null */ public static List countriesByLanguage(String languageCode) { List countries = (List) cCountriesByLanguage.get(languageCode); //syncd if (countries == null) { if (languageCode != null) { countries = new ArrayList(); List locales = availableLocaleList(); for (int i = 0; i < locales.size(); i++) { Locale locale = (Locale) locales.get(i); if (languageCode.equals(locale.getLanguage()) && locale.getCountry().length() != 0 && locale.getVariant().length() == 0) { countries.add(locale); } } countries = Collections.unmodifiableList(countries); } else { countries = Collections.EMPTY_LIST; } cCountriesByLanguage.put(languageCode, countries); //syncd } return countries; } }