code: private static SimpleDateFormat buildDateFormat(final String pattern) {
  
      SimpleDateFormat simpleDateFormat = simpleDateFormatCache.get();
      if (simpleDateFormat == null) {
        simpleDateFormat = new SimpleDateFormat();
        simpleDateFormatCache.set(simpleDateFormat);
      }
      simpleDateFormat.applyPattern(pattern);
      return simpleDateFormat;
    }
docs: Get a SimpleDateFormat object by given pattern.
  
  @param pattern date format pattern.
  @return a SimpleDateFormat object by given pattern.