selectPreferredLanguage

Description

Inspects the request’s Accept-Language header and determines, which of a given set of language alternatives is preferred by the client according to content negotiation rules defined by http://tools.ietf.org/html/rfc7231#section-5.3.5.

If there are several best language alternatives that the client has equal preference for (even if this preference is zero!) the order of the arguments is used as a tie breaker (first one wins).

Example

final Route enRoute = selectPreferredLanguage(
  Arrays.asList(Language.create("en"), Language.create("en-US")), lang ->
    complete(lang.toString())
);
final Route deHuRoute = selectPreferredLanguage(
  Arrays.asList(Language.create("de-DE"), Language.create("hu")), lang ->
    complete(lang.toString())
);


// tests:
final HttpRequest request = HttpRequest.GET("/").addHeader(AcceptLanguage.create(
  Language.create("en-US").withQValue(1f),
  Language.create("en").withQValue(0.7f),
  LanguageRanges.ALL.withQValue(0.1f),
  Language.create("de-DE").withQValue(0.5f)
));

testRoute(enRoute).run(request).assertEntity("en-US");
testRoute(deHuRoute).run(request).assertEntity("de-DE");