code: public static Collection<Locale> getLocales(final HttpServletRequest req) {
      if (req.getHeader("Accept-Language") == null) {
        return null;
      }
  
      @SuppressWarnings("unchecked")
      Enumeration<Locale> lcs = req.getLocales();
      ArrayList<Locale> locales = new ArrayList<Locale>();
      while (lcs.hasMoreElements()) {
        locales.add(lcs.nextElement());
      }
  
      return locales;
    }
docs: If there is no Accept-Language header returns null, otherwise returns a
  collection of Locales ordered with preferred first.
  
  @param req
  @return Collection of locales or null