private String getHistoryDirDatePart(long timeInMillis) {
    Calendar timestamp = Calendar.getInstance(_timeZone);
    timestamp.setTimeInMillis(timeInMillis);
    String datePart = String.format(TIMESTAMP_DIR_FORMAT,
        timestamp.get(Calendar.YEAR),
        timestamp.get(Calendar.MONTH) + 1,
        timestamp.get(Calendar.DAY_OF_MONTH));
    return StringUtils.join(new String[]{_historyLocation, datePart, ""}, File.separator);
  }
The location of a job history file is in format: {done-dir}/yyyy/mm/dd/{serialPart}.
yyyy/mm/dd is the year, month and date of the finish time.
serialPart is the first 6 digits of the serial number considering it as a 9 digits number.
PS: The serial number is the last part of an app id.
<p>
For example, if appId = application_1461566847127_84624, then serial number is 84624.
Consider it as a 9 digits number, serial number is 000084624. So the corresponding
serialPart is 000084. If this application finish at 2016-5-30, its history file will locate
at {done-dir}/2016/05/30/000084
</p>
<p>
Furthermore, this location format is only satisfied for finished jobs in {done-dir} and not
for running jobs in {intermediate-done-dir}.
</p>
app/com/linkedin/drelephant/mapreduce/fetchers/MapReduceFSFetcherHadoop2.java