What is the best way to increment a Java.sql.date / time?

Question

I have an issue where I have a MySQL database storing dates and times in separate columns. However, in Java code I need to increment the resulting timestamp for a date and t

Answer 1

You can use Joda time. Then, you can use DateTime's plusHours, plusDays, and plusWeeks. For parsing, there is DateTimeFormat and DateTimeFormatter. Something like:

DateTimeFormatter fmt = DateTimeFormat.forPattern("YYYY-MM-dd HH:mm:ss");
DateTime dt = fmt.parseDateTime(timestampin);

if (increment.equals("HOURLY")) {
    dt = dt.plusHours(1);
}
else if (increment.equals("DAILY")) {
    dt = dt.plusDays(1);
}
else  if (increment.equals("WEEKLY")) {
    dt = dt.plusWeeks(1);
}

String timestampOut = fmt.print(dt);

You can probably use something like:

DateTime dt = new DateMidnight(sqlDate).plus(Period.millis(sqlTime.getTime()));

That assumes the sql.Time represents the number of milliseconds since midnight.

Answer 2

Here's an optimization, assuming that the input is java.util.Date wherein you can just pass java.sql.Date and java.sql.Time in since they are just its subclasses.

public static String addToDateTime(Date date, Increment increment) throws ParseException {
    Calendar calendar = calendar.getInstance();
    calendar.clear();
    calendar.setTime(date);

    switch (increment) {
        case HOURLY: calendar.add(Calendar.HOUR, 1); break;
        case DAILY: calendar.add(Calendar.DATE, 1); break;
        case WEEKLY: calendar.add(Calendar.WEEK_OF_YEAR, 1); break;
        case DO_NOT_POLL: break;
    }

    return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(calendar.getTime());
}

public enum Increment {
    HOURLY, DAILY, WEEKLY, DO_NOT_POLL;
}

which can be used as

String newTimestamp = addToDateTime(timestampIn, Increment.WEEKLY);

To learn more about the useful enum, check the Sun tutorial on the subject. However, as per Java 7 you should be able to switch on String.

---

I however strongly agree the JodaTime advice, here's an example:

public static String addToDateTime(Date date, Increment increment) {
    DateTime dt = new DateTime(date);

    switch (increment) {
        case HOURLY: dt = dt.plusHours(1); break;
        case DAILY: dt = dt.plusDays(1); break;
        case WEEKLY: dt = dt.plusWeeks(1); break;
        case DO_NOT_POLL: break;
    }

    return df.print(dt);
}

public enum Increment {
    HOURLY, DAILY, WEEKLY, DO_NOT_POLL;
}

The difference is admittedly not shocking, but it has more advantages as well.