public static boolean isADateFormat(Short formatIndex, String formatString) {
        if (formatIndex == null) {
            return false;
        }
        Map<Short, Boolean> isDateCache = DATE_THREAD_LOCAL.get();
        if (isDateCache == null) {
            isDateCache = MapUtils.newHashMap();
            DATE_THREAD_LOCAL.set(isDateCache);
        } else {
            Boolean isDatecachedDataList = isDateCache.get(formatIndex);
            if (isDatecachedDataList != null) {
                return isDatecachedDataList;
            }
        }
        boolean isDate = isADateFormatUncached(formatIndex, formatString);
        isDateCache.put(formatIndex, isDate);
        return isDate;
    }
Determine if it is a date format.

@param formatIndex
@param formatString
@return
fastexcel-core/src/main/java/cn/idev/excel/util/DateUtils.java