Some date time related gists

DateTimeGist.java

// Check leap year
public boolean isLeapYear(int year) {
    boolean leapYear = false;
    if (year % 4 == 0) {
        if (year % 100 == 0) {
            if ( year % 400 == 0) {
               leapYear = true;
            }       
        } else {
           leapYear = true;
        }
    }
    return leapYear;
}

public static String getHistoryTimeStamp(int historyKeepDays) {
    final String HISTORY_DATETIME_FORMMAT = "yyyyMMdd.HH:mm:ss.SSSZ";
    Date today = new Date();
    Calendar cal = new GregorianCalendar();
    cal.setTime(today);
    cal.add(Calendar.DAY_OF_MONTH, -historyKeepDays);
    DateFormat dateFormat = new SimpleDateFormat(HISTORY_DATETIME_FORMMAT, Locale.US);
    return dateFormat.format(cal.getTime());
}