问题
The accept-language header in request is usually a long complex string -
Eg.
Accept-Language : en-ca,en;q=0.8,en-us;q=0.6,de-de;q=0.4,de;q=0.2
Is there a simple way to parse it in java? Or a API to help me do that?
回答1:
I would suggest using ServletRequest.getLocales() to let the container parse Accept-Language rather than trying to manage the complexity yourself.
回答2:
For the record, now it is possible with Java 8:
Locale.LanguageRange.parse()
回答3:
Here's an alternative way to parse the Accept-Language header which doesn't require a servlet container:
String header = "en-ca,en;q=0.8,en-us;q=0.6,de-de;q=0.4,de;q=0.2";
for (String str : header.split(",")){
String[] arr = str.trim().replace("-", "_").split(";");
//Parse the locale
Locale locale = null;
String[] l = arr[0].split("_");
switch(l.length){
case 2: locale = new Locale(l[0], l[1]); break;
case 3: locale = new Locale(l[0], l[1], l[2]); break;
default: locale = new Locale(l[0]); break;
}
//Parse the q-value
Double q = 1.0D;
for (String s : arr){
s = s.trim();
if (s.startsWith("q=")){
q = Double.parseDouble(s.substring(2).trim());
break;
}
}
//Print the Locale and associated q-value
System.out.println(q + " - " + arr[0] + "\t " + locale.getDisplayLanguage());
}
You can find an explanation of the Accept-Language header and associated q-values here:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
Many thanks to Karl Knechtel and Mike Samuel. Thier comments to the original question helped point me in the right direction.
回答4:
ServletRequest.getLocale() is certainly the best option if it is available and not overwritten as some frameworks do.
For all other cases Java 8 offers Locale.LanguageRange.parse() as previously mentioned by Quiang Li. This however only gives back a Language String, not a Locale. To parse the language strings you can use Locale.forLanguageTag() (available since Java 7):
final List<Locale> acceptedLocales = new ArrayList<>();
final String userLocale = request.getHeader("Accept-Language");
if (userLocale != null) {
final List<LanguageRange> ranges = Locale.LanguageRange.parse(userLocale);
if (ranges != null) {
ranges.forEach(languageRange -> {
final String localeString = languageRange.getRange();
final Locale locale = Locale.forLanguageTag(localeString);
acceptedLocales.add(locale);
});
}
}
return acceptedLocales;
回答5:
We are using Spring boot and Java 8. This works
In ApplicationConfig.java write this
@Bean
public LocaleResolver localeResolver() {
return new SmartLocaleResolver();
}
and I have this list in my constants class that has languages that we support
List<Locale> locales = Arrays.asList(new Locale("en"),
new Locale("es"),
new Locale("fr"),
new Locale("es", "MX"),
new Locale("zh"),
new Locale("ja"));
and write the logic in the below class.
public class SmartLocaleResolver extends AcceptHeaderLocaleResolver {
@Override
public Locale resolveLocale(HttpServletRequest request) {
if (StringUtils.isBlank(request.getHeader("Accept-Language"))) {
return Locale.getDefault();
}
List<Locale.LanguageRange> ranges = Locale.LanguageRange.parse("da,es-MX;q=0.8");
Locale locale = Locale.lookup(ranges, locales);
return locale ;
}
}
回答6:
The above solutions lack some kind of validation. Using ServletRequest.getLocale() returns the server locale if the user does not provides a valid one.
Our websites lately received spam requests with various Accept-Language heades like:
secret.google.como-o-8-o-o.com search shell is much better than google!Google officially recommends o-o-8-o-o.com search shell!Vitaly rules google ☆*:｡゜ﾟ･*ヽ(^ᴗ^)ﾉ*･゜ﾟ｡:*☆ ¯\_(ツ)_/¯(ಠ益ಠ)(ಥ‿ಥ)(ʘ‿ʘ)ლ(ಠ_ಠლ)( ͡° ͜ʖ ͡°)ヽ(ﾟДﾟ)ﾉʕ•̫͡•ʔᶘ ᵒᴥᵒᶅ(=^ ^=)oO
This implementation can optional check against a supported list of valid Locale. Without this check a simple request with "test" or (2, 3, 4) still bypass the syntax-only validation of LanguageRange.parse(String).
It optional allows empty and null values to allow search engine crawler.
Servlet Filter
final String headerAcceptLanguage = request.getHeader("Accept-Language");
// check valid
if (!HttpHeaderUtils.isHeaderAcceptLanguageValid(headerAcceptLanguage, true, Locale.getAvailableLocales()))
return;
Utility
/**
* Checks if the given accept-language request header can be parsed.<br>
* <br>
* Optional the parsed LanguageRange's can be checked against the provided
* <code>locales</code> so that at least one locale must match.
*
* @see LanguageRange#parse(String)
*
* @param acceptLanguage
* @param isBlankValid Set to <code>true</code> if blank values are also
* valid
* @param locales Optional collection of valid Locale to validate any
* against.
*
* @return <code>true</code> if it can be parsed
*/
public static boolean isHeaderAcceptLanguageValid(final String acceptLanguage, final boolean isBlankValid,
final Locale[] locales)
{
// allow null or empty
if (StringUtils.isBlank(acceptLanguage))
return isBlankValid;
try
{
// check syntax
final List<LanguageRange> languageRanges = Locale.LanguageRange.parse(acceptLanguage);
// wrong syntax
if (languageRanges.isEmpty())
return false;
// no valid locale's to check against
if (ArrayUtils.isEmpty(locales))
return true;
// check if any valid locale exists
for (final LanguageRange languageRange : languageRanges)
{
final Locale locale = Locale.forLanguageTag(languageRange.getRange());
// validate available locale
if (ArrayUtils.contains(locales, locale))
return true;
}
return false;
}
catch (final Exception e)
{
return false;
}
}
回答7:
Locale.forLanguageTag("en-ca,en;q=0.8,en-us;q=0.6,de-de;q=0.4,de;q=0.2")
来源：https://stackoverflow.com/questions/6824157/parse-accept-language-header-in-java