public static String format(long millis) {
    return format(millis, getPattern());
}

public static String format(Date date) {
    return format(date, getPattern());
}

public static String format(long millis, String pattern) {
        return format(new Date(millis), pattern);
}

public static String format(Date date, String pattern) {
    if (date == null) {
        return null;
    }
    SimpleDateFormat formatter = new SimpleDateFormat(pattern);
    return formatter.format(date);
}