public static long parseUnknownString(final String date) {
        if (!looksLikeDate(date)) {
            Long.parseLong(date);
        }

        try {
            // Try and parse the string an a standard ISO8601 date.
            final ZonedDateTime dateTime = parse(NORMAL_STROOM_TIME_FORMATTER, date, ZoneOffset.UTC);
            return dateTime.toInstant().toEpochMilli();

        } catch (final Exception e) {
            // If we were unable to parse the value as an ISO8601 date then try
            // and get it as a long.
            return Long.parseLong(date);
        }
    }
Parse a 'file' type date.

@param date string date
@return date as milliseconds since epoch
@throws IllegalArgumentException if date does not parse
stroom-legacy/stroom-legacy-model_6_1/src/main/java/stroom/legacy/model_6_1/DateUtil.java