Question

The problem is the SimpleDateFormat seems to be adding 17 hours to the actual timestamp.

This should be something really simple. I’m not sure what I’m doing wrong. I have a method that will convert a long of nanoseconds to a formatted timestamp. It’s adding 17 hours. Here’s my SSCCE

package playground;

import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.concurrent.TimeUnit;

/**
*
* @author kentcdodds
*/
public class NanosecondsToString {

  public static void main(String[] args) {
    long nanoseconds = 234236402;
    Timestamp ts = new Timestamp(TimeUnit.MILLISECONDS.convert(nanoseconds, TimeUnit.NANOSECONDS));
    SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss:SSS");
    String formatted = format.format(ts);
    System.out.println(formatted);
  }
}

The output: 17:00:00:234

I’m in Mountain Standard Time

Answer 1

You have to set the timezone to UTC.

public static void main(String[] args) throws IOException {
              long nanoseconds = 234236402;
              Timestamp ts = new Timestamp(TimeUnit.MILLISECONDS.convert(nanoseconds, TimeUnit.NANOSECONDS));
              SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss:SSS");
              format.setTimeZone(TimeZone.getTimeZone("UTC"));
              String formatted = format.format(ts);
              System.out.println(formatted);
    }

SimpleDateFormat will convert the timestamp to a time in your current time zone by default. So it is necessary to tell it to assume it as UTC. Otherwise, you can use jodatime’s interval class.