org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver Maven / Gradle / Ivy
/*
* Copyright 2002-2023 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 jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.LocaleResolver;
/**
* {@link LocaleResolver} implementation that looks for a match between locales
* in the {@code Accept-Language} header and a list of configured supported
* locales.
*
* See {@link #setSupportedLocales(List)} for further details on how
* supported and requested locales are matched.
*
*
Note: This implementation does not support {@link #setLocale} since the
* {@code Accept-Language} header can only be changed by changing the client's
* locale settings.
*
* @author Juergen Hoeller
* @author Rossen Stoyanchev
* @since 27.02.2003
* @see jakarta.servlet.http.HttpServletRequest#getLocale()
*/
public class AcceptHeaderLocaleResolver extends AbstractLocaleResolver {
private final List supportedLocales = new ArrayList<>(4);
/**
* Configure the list of supported locales to compare and match against
* {@link HttpServletRequest#getLocales() requested locales}.
* In order for a supported locale to be considered a match, it must match
* on both country and language. If you want to support a language-only match
* as a fallback, you must configure the language explicitly as a supported
* locale.
*
For example, if the supported locales are {@code ["de-DE","en-US"]},
* then a request for {@code "en-GB"} will not match, and neither will a
* request for {@code "en"}. If you want to support additional locales for a
* given language such as {@code "en"}, then you must add it to the list of
* supported locales.
*
If there is no match, then the {@link #setDefaultLocale(Locale)
* defaultLocale} is used, if configured, or otherwise falling back on
* {@link HttpServletRequest#getLocale()}.
* @param locales the supported locales
* @since 4.3
*/
public void setSupportedLocales(List locales) {
this.supportedLocales.clear();
this.supportedLocales.addAll(locales);
}
/**
* Get the configured list of supported locales.
* @since 4.3
*/
public List getSupportedLocales() {
return this.supportedLocales;
}
@Override
public Locale resolveLocale(HttpServletRequest request) {
Locale defaultLocale = getDefaultLocale();
if (defaultLocale != null && request.getHeader("Accept-Language") == null) {
return defaultLocale;
}
Locale requestLocale = request.getLocale();
List 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 supportedLocales) {
Enumeration 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 supportedLocale : supportedLocales) {
if (!StringUtils.hasLength(supportedLocale.getCountry()) &&
supportedLocale.getLanguage().equals(locale.getLanguage())) {
languageMatch = supportedLocale;
break;
}
}
}
}
return languageMatch;
}
@Override
public void setLocale(HttpServletRequest request, @Nullable HttpServletResponse response, @Nullable Locale locale) {
throw new UnsupportedOperationException(
"Cannot change HTTP Accept-Language header - use a different locale resolution strategy");
}
}