Java: How to add seconds to Timestamp?

The code you've got works for me. As a short but complete program:

import java.util.*;
import java.sql.*;

public class Test {
    public static void main(String[] args) {
        long retryDate = System.currentTimeMillis();

        int sec = 600;

        Timestamp original = new Timestamp(retryDate);
        Calendar cal = Calendar.getInstance();
        cal.setTimeInMillis(original.getTime());
        cal.add(Calendar.SECOND, sec);
        Timestamp later = new Timestamp(cal.getTime().getTime());

        System.out.println(original);
        System.out.println(later);
    }
}

Output:

2011-11-07 10:27:45.302
2011-11-07 10:37:45.302

Note the difference of 10 minutes, i.e. 600 seconds.

Of course you lose the sub-millisecond precision this way, which may well not be ideal - and it goes against what I'm normally use a timestamp for in the first place - but it does add the seconds...

Another option would be to just use Timestamp directly:

Timestamp original = ...;
Timestamp later = new Timestamp(original.getTime() + (sec * 1000L));
later.setNanos(original.getNanos());

I've always favoured brevity:

int sec = 600;

Timestamp later = new Timestamp(retry_date.getTime() + sec * 1000);

or if you want relative to "now":

Timestamp later = new Timestamp(System.currentTimeMillis() + sec * 1000);