org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver.java Source code

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Here is the source code for org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver.java

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/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed 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.springframework.web.servlet.i18n;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.Locale;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.LocaleResolver;

/**
 * {@link LocaleResolver} implementation that simply uses the primary locale
 * specified in the "accept-language" header of the HTTP request (that is,
 * the locale sent by the client browser, normally that of the client's OS).
 *
 * <p>Note: Does not support {@code setLocale}, since the accept header
 * can only be changed through changing the client's locale settings.
 *
 * @author Juergen Hoeller
 * @author Rossen Stoyanchev
 * @since 27.02.2003
 * @see javax.servlet.http.HttpServletRequest#getLocale()
 */
public class AcceptHeaderLocaleResolver implements LocaleResolver {

    private final List<Locale> supportedLocales = new ArrayList<>(4);

    @Nullable
    private Locale defaultLocale;

    /**
     * Configure supported locales to check against the requested locales
     * determined via {@link HttpServletRequest#getLocales()}. If this is not
     * configured then {@link HttpServletRequest#getLocale()} is used instead.
     * @param locales the supported locales
     * @since 4.3
     */
    public void setSupportedLocales(List<Locale> locales) {
        this.supportedLocales.clear();
        this.supportedLocales.addAll(locales);
    }

    /**
     * Return the configured list of supported locales.
     * @since 4.3
     */
    public List<Locale> getSupportedLocales() {
        return this.supportedLocales;
    }

    /**
     * Configure a fixed default locale to fall back on if the request does not
     * have an "Accept-Language" header.
     * <p>By default this is not set in which case when there is "Accept-Language"
     * header, the default locale for the server is used as defined in
     * {@link HttpServletRequest#getLocale()}.
     * @param defaultLocale the default locale to use
     * @since 4.3
     */
    public void setDefaultLocale(@Nullable Locale defaultLocale) {
        this.defaultLocale = defaultLocale;
    }

    /**
     * The configured default locale, if any.
     * @since 4.3
     */
    @Nullable
    public Locale getDefaultLocale() {
        return this.defaultLocale;
    }

    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        Locale defaultLocale = getDefaultLocale();
        if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
            return defaultLocale;
        }
        Locale requestLocale = request.getLocale();
        List<Locale> supportedLocales = getSupportedLocales();
        if (supportedLocales.isEmpty() || supportedLocales.contains(requestLocale)) {
            return requestLocale;
        }
        Locale supportedLocale = findSupportedLocale(request, supportedLocales);
        if (supportedLocale != null) {
            return supportedLocale;
        }
        return (defaultLocale != null ? defaultLocale : requestLocale);
    }

    @Nullable
    private Locale findSupportedLocale(HttpServletRequest request, List<Locale> supportedLocales) {
        Enumeration<Locale> requestLocales = request.getLocales();
        Locale languageMatch = null;
        while (requestLocales.hasMoreElements()) {
            Locale locale = requestLocales.nextElement();
            if (supportedLocales.contains(locale)) {
                if (languageMatch == null || languageMatch.getLanguage().equals(locale.getLanguage())) {
                    // Full match: language + country, possibly narrowed from earlier language-only match
                    return locale;
                }
            } else if (languageMatch == null) {
                // Let's try to find a language-only match as a fallback
                for (Locale candidate : supportedLocales) {
                    if (!StringUtils.hasLength(candidate.getCountry())
                            && candidate.getLanguage().equals(locale.getLanguage())) {
                        languageMatch = candidate;
                        break;
                    }
                }
            }
        }
        return languageMatch;
    }

    @Override
    public void setLocale(HttpServletRequest request, @Nullable HttpServletResponse response,
            @Nullable Locale locale) {
        throw new UnsupportedOperationException(
                "Cannot change HTTP accept header - use a different locale resolution strategy");
    }

}