How do I increment a java.sql.Timestamp by 14 days?

Question

I have an app that takes a Timestamp as a boundary for the start date and end date of a sql selection, I want to populate a hashmap with weeks this year since the first monday of the year as the values and the week number as the keys. I'm finding it really hard to work with timestamps and I don't feel very good about adding 86,400,000 seconds to it to increment the day, as this doesn't account for the leap days, hours, seconds.

I plan on adding 13 days 23 hours, 59 minutes and 59 seconds to it so that I can lookup the start date in the map by the week as the key, then use the start date to get the end date.

So I'm looking to try to get something like this:

Week  startDate              endDate
1     2011-01-03 00:00:00    2011-01-16 23:59:59
2     2011-01-17 00:00:00    2011-01-30 23:59:59

With the first two columns in the Map and the last one being calculated after looking it up. How do I safely increment a java.sql.Timestamp?

Answer 1

It worth noting that 14 days is not always 14 * 24 * 3600 seconds. When you have daylight savings, this can be an hour shorter or longer. Historically it can be much more complex than that.

Instead I would suggest using JodaTime or the Calendar to perform the time zone dependant calculation.

Answer 2

java.sql.Timestamp ts = ...
Calendar cal = Calendar.getInstance();
cal.setTime(ts);
cal.add(Calendar.DAY_OF_WEEK, 14);
ts.setTime(cal.getTime().getTime()); // or
ts = new Timestamp(cal.getTime().getTime());

This will correctly cater for daylight-time transitions in your default Timezone. You can tell the Calendar class to use a different Timezone if need be.

Answer 3

Java 8

Timestamp old;
ZonedDateTime zonedDateTime = old.toInstant().atZone(ZoneId.of("UTC"));
Timestamp new = Timestamp.from(zonedDateTime.plus(14, ChronoUnit.DAYS).toInstant());

Answer 4

private Long dayToMiliseconds(int days){
    Long result = Long.valueOf(days * 24 * 60 * 60 * 1000);
    return result;
}

public Timestamp addDays(int days, Timestamp t1) throws Exception{
    if(days < 0){
        throw new Exception("Day in wrong format.");
    }
    Long miliseconds = dayToMiliseconds(days);
    return new Timestamp(t1.getTime() + miliseconds);
}