LocaleUtils.java

/*
 * 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
 *
 *      https://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.
 */

package org.apache.commons.lang3;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * Operations to assist when working with a {@link Locale}.
 *
 * <p>
 * This class tries to handle {@code null} input gracefully. An exception will not be thrown for a {@code null} input. Each method documents its behavior in
 * more detail.
 * </p>
 *
 * @see Locale
 * @since 2.2
 */
public class LocaleUtils {

    /**
     * Avoids synchronization, initializes on demand.
     */
    private static final class SyncAvoid {

        /** Private unmodifiable and sorted list of available locales. */
        private static final List<Locale> AVAILABLE_LOCALE_ULIST;

        /** Private unmodifiable set of available locales. */
        private static final Set<Locale> AVAILABLE_LOCALE_USET;
        static {
            AVAILABLE_LOCALE_ULIST = Collections
                    .unmodifiableList(Arrays.asList(ArraySorter.sort(Locale.getAvailableLocales(), Comparator.comparing(Locale::toString))));
            AVAILABLE_LOCALE_USET = Collections.unmodifiableSet(new LinkedHashSet<>(AVAILABLE_LOCALE_ULIST));
        }
    }

    /**
     * The underscore character {@code '}{@value}{@code '}.
     */
    private static final char UNDERSCORE = '_';

    /**
     * The undetermined language {@value}.
     * <p>
     * If a language is empty, or not <em>well-formed</em> (for example "a" or "e2"), {@link Locale#toLanguageTag()} will return {@code "und"} (Undetermined).
     * </p>
     *
     * @see Locale#toLanguageTag()
     */
    private static final String UNDETERMINED = "und";

    /**
     * The dash character {@code '}{@value}{@code '}.
     */
    private static final char DASH = '-';

    /**
     * Concurrent map of language locales by country.
     */
    private static final ConcurrentMap<String, List<Locale>> cLanguagesByCountry = new ConcurrentHashMap<>();

    /**
     * Concurrent map of country locales by language.
     */
    private static final ConcurrentMap<String, List<Locale>> cCountriesByLanguage = new ConcurrentHashMap<>();

    /**
     * Obtains an unmodifiable and sorted list of installed locales.
     *
     * <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 and sorted list of available locales.
     */
    public static List<Locale> availableLocaleList() {
        return SyncAvoid.AVAILABLE_LOCALE_ULIST;
    }

    private static List<Locale> availableLocaleList(final Predicate<Locale> predicate) {
        return availableLocaleList().stream().filter(predicate).collect(Collectors.toList());
    }

    /**
     * Obtains an unmodifiable set of installed locales.
     *
     * <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<Locale> availableLocaleSet() {
        return SyncAvoid.AVAILABLE_LOCALE_USET;
    }

    /**
     * Obtains the list of countries supported for a given language.
     *
     * <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, not null.
     */
    public static List<Locale> countriesByLanguage(final String languageCode) {
        if (languageCode == null) {
            return Collections.emptyList();
        }
        return cCountriesByLanguage.computeIfAbsent(languageCode, lc -> Collections
                .unmodifiableList(availableLocaleList(locale -> languageCode.equals(locale.getLanguage()) && !hasCountry(locale) && hasVariant(locale))));
    }

    /**
     * Tests whether the given Locale defines a variant.
     *
     * @param locale The Locale to test.
     * @return whether the given Locale defines a variant.
     */
    private static boolean hasCountry(final Locale locale) {
        return locale.getCountry().isEmpty();
    }

    /**
     * Tests whether the given Locale defines a country.
     *
     * @param locale The Locale to test.
     * @return whether the given Locale defines a country.
     */
    private static boolean hasVariant(final Locale locale) {
        return locale.getVariant().isEmpty();
    }

    /**
     * Tests whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
     *
     * @param str The string to test.
     * @return whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
     */
    private static boolean isAlpha2Len(final String str) {
        return str.length() == 2;
    }

    /**
     * Tests whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-3 country code.
     *
     * @param str The string to test.
     * @return whether the given string is the length of an <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-3 country code.
     */
    private static boolean isAlpha3Len(final String str) {
        return str.length() == 3;
    }

    /**
     * Checks if the locale specified is in the set of available locales.
     *
     * @param locale the Locale object to check if it is available.
     * @return true if the locale is a known locale.
     */
    public static boolean isAvailableLocale(final Locale locale) {
        return availableLocaleSet().contains(locale);
    }

    /**
     * Tests whether the given String is a <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> alpha-2 country code.
     *
     * @param str the String to check.
     * @return true, is the given String is a <a href="https://www.iso.org/iso-3166-country-codes.html">ISO 3166</a> compliant country code.
     */
    private static boolean isISO3166CountryCode(final String str) {
        return StringUtils.isAllUpperCase(str) && isAlpha2Len(str);
    }

    /**
     * Tests whether the given String is a <a href="https://www.iso.org/iso-639-language-code">ISO 639</a> compliant language code.
     *
     * @param str the String to check.
     * @return true, if the given String is a <a href="https://www.iso.org/iso-639-language-code">ISO 639</a> compliant language code.
     */
    private static boolean isISO639LanguageCode(final String str) {
        return StringUtils.isAllLowerCase(str) && (isAlpha2Len(str) || isAlpha3Len(str));
    }

    /**
     * Tests whether a Locale's language is undetermined.
     * <p>
     * A Locale's language tag is undetermined if it's value is {@code "und"}. If a language is empty, or not well-formed (for example, "a" or "e2"), it will be
     * equal to {@code "und"}.
     * </p>
     *
     * @param locale the locale to test.
     * @return whether a Locale's language is undetermined.
     * @see Locale#toLanguageTag()
     * @since 3.14.0
     */
    public static boolean isLanguageUndetermined(final Locale locale) {
        return locale == null || UNDETERMINED.equals(locale.toLanguageTag());
    }

    /**
     * TestsNo whether the given String is a UN M.49 numeric area code.
     *
     * @param str the String to check.
     * @return true, is the given String is a UN M.49 numeric area code.
     */
    private static boolean isNumericAreaCode(final String str) {
        return StringUtils.isNumeric(str) && isAlpha3Len(str);
    }

    /**
     * Obtains the list of languages supported for a given country.
     *
     * <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, not null.
     */
    public static List<Locale> languagesByCountry(final String countryCode) {
        if (countryCode == null) {
            return Collections.emptyList();
        }
        return cLanguagesByCountry.computeIfAbsent(countryCode,
                k -> Collections.unmodifiableList(availableLocaleList(locale -> countryCode.equals(locale.getCountry()) && hasVariant(locale))));
    }

    /**
     * Obtains the list of locales to search through when performing a locale search.
     *
     * <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, not null.
     */
    public static List<Locale> localeLookupList(final Locale locale) {
        return localeLookupList(locale, locale);
    }

    /**
     * Obtains the list of locales to search through when performing a locale search.
     *
     * <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, not null.
     */
    public static List<Locale> localeLookupList(final Locale locale, final Locale defaultLocale) {
        final List<Locale> list = new ArrayList<>(4);
        if (locale != null) {
            list.add(locale);
            if (!hasVariant(locale)) {
                list.add(new Locale(locale.getLanguage(), locale.getCountry()));
            }
            if (!hasCountry(locale)) {
                list.add(new Locale(locale.getLanguage(), StringUtils.EMPTY));
            }
            if (!list.contains(defaultLocale)) {
                list.add(defaultLocale);
            }
        }
        return Collections.unmodifiableList(list);
    }

    /**
     * Creates new {@linkplain Locale} for the given country.
     *
     * @param country An ISO 3166 alpha-2 country code or a UN M.49 numeric-3 area code. See the {@linkplain Locale} class description about valid country
     *                values.
     * @throws NullPointerException thrown if either argument is null.
     * @return a new new Locale for the given country.
     * @see Locale#Locale(String, String)
     */
    static Locale ofCountry(final String country) {
        return new Locale(StringUtils.EMPTY, country);
    }

    /**
     * Tries to parse a Locale from the given String.
     * <p>
     * See {@link Locale} for the format.
     * </p>
     *
     * @param str the String to parse as a Locale.
     * @return a Locale parsed from the given String.
     * @throws IllegalArgumentException if the given String cannot be parsed.
     * @see Locale
     * @see <a href="https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor">Locale special cases</a>
     */
    private static Locale parseLocale(final String str) {
        if (isISO639LanguageCode(str)) {
            return new Locale(str);
        }
        final int limit = 3;
        final char separator = str.indexOf(UNDERSCORE) != -1 ? UNDERSCORE : DASH;
        final String[] segments = str.split(String.valueOf(separator), 3);
        final String language = segments[0];
        if (segments.length == 2) {
            final String country = segments[1];
            if (isISO639LanguageCode(language) && isISO3166CountryCode(country) || isNumericAreaCode(country)) {
                return new Locale(language, country);
            }
        } else if (segments.length == limit) {
            final String country = segments[1];
            final String variant = segments[2];
            // Special case 1: https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor
            if (str.equals("th_TH_TH_#u-nu-thai")) {
                return new Locale(language, country, "TH");
            }
            // Special case 2: https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor
            if (str.equals("ja_JP_JP_#u-ca-japanese")) {
                return new Locale(language, country, "JP");
            }
            if (isISO639LanguageCode(language) && (country.isEmpty() || isISO3166CountryCode(country) || isNumericAreaCode(country)) && !variant.isEmpty()) {
                return new Locale(language, country, variant);
            }
        }
        if (ArrayUtils.contains(Locale.getISOCountries(), str)) {
            return new Locale(StringUtils.EMPTY, str);
        }
        throw new IllegalArgumentException("Invalid locale format: " + str);
    }

    /**
     * Returns the given locale if non-{@code null}, otherwise {@link Locale#getDefault()}.
     *
     * @param locale a locale or {@code null}.
     * @return the given locale if non-{@code null}, otherwise {@link Locale#getDefault()}.
     * @since 3.12.0
     */
    public static Locale toLocale(final Locale locale) {
        return locale != null ? locale : Locale.getDefault();
    }

    /**
     * Converts a String to a Locale.
     *
     * <p>
     * This method takes the string format of a locale and creates the locale object from it.
     * </p>
     *
     * <pre>
     *   LocaleUtils.toLocale("")           = new Locale("", "")
     *   LocaleUtils.toLocale("en")         = new Locale("en", "")
     *   LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")
     *   LocaleUtils.toLocale("en-GB")      = new Locale("en", "GB")
     *   LocaleUtils.toLocale("en_001")     = new Locale("en", "001")
     *   LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)
     *   LocaleUtils.toLocale("US")         = new Locale("", "US") // Because "US" is Locale.getISOCountries()
     * </pre>
     *
     * <p>
     * (#) The behavior 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 or
     * a dash. 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.
     * @see Locale#forLanguageTag(String)
     * @see Locale#getISOCountries()
     * @see <a href="https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Locale.html#special_cases_constructor">Locale special cases</a>
     */
    public static Locale toLocale(final String str) {
        if (str == null) {
            // TODO Should this return the default locale?
            return null;
        }
        if (str.isEmpty()) { // LANG-941 - JDK 8 introduced an empty locale where all fields are blank
            return new Locale(StringUtils.EMPTY, StringUtils.EMPTY);
        }
        final int len = str.length();
        if (len < 2) {
            throw new IllegalArgumentException("Invalid locale format: " + str);
        }
        final char ch0 = str.charAt(0);
        if (ch0 == UNDERSCORE || ch0 == DASH) {
            if (len < 3) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            final char ch1 = str.charAt(1);
            final char ch2 = str.charAt(2);
            if (!Character.isUpperCase(ch1) || !Character.isUpperCase(ch2)) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            if (len == 3) {
                return new Locale(StringUtils.EMPTY, str.substring(1, 3));
            }
            if (len < 5) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            if (str.charAt(3) != ch0) {
                throw new IllegalArgumentException("Invalid locale format: " + str);
            }
            return new Locale(StringUtils.EMPTY, str.substring(1, 3), str.substring(4));
        }
        return parseLocale(str);
    }

    /**
     * {@link LocaleUtils} instances should NOT be constructed in standard programming. Instead, the class should be used as
     * {@code LocaleUtils.toLocale("en_GB");}.
     *
     * <p>
     * This constructor is public to permit tools that require a JavaBean instance to operate.
     * </p>
     *
     * @deprecated TODO Make private in 4.0.
     */
    @Deprecated
    public LocaleUtils() {
        // empty
    }
}