How to get ISO week number?

Question

hi,
I need to interact with a server that expects to be passed the ISO week number. The Calendar class doesn't seem to support this though (although the documentation claims that it is ISO 8601 compliant).
For instance the web page here gives today (Jan 10th 2005) as being in Week 2
http://personal.ecu.edu/mccartyr/isowdcal.html
but this code snippet returns "Week 3"
import java.util.*;
public class WeekOfYear {
     public static void main(String[]arg) {
          Calendar c = Calendar.getInstance();
          System.out.println("Week "+c.get(Calendar.WEEK_OF_YEAR));
}does anyone know a correct way of getting the ISO 8601 Week number without reimplenting a lot of delicate code?
thanks,
asjf
ps. of course for now, and the rest of 2005, i'm going to hard code subtracting 1 as a gratuitous hack :o)

Answer 1

hi,
thanks - i did check the docs :)
the problem is that Calendar's idea of what the first week in the year is differs from the ISO standard
the problem is that the ISO standard defines the first week of the year as that containing the first Thursday (ie some days may become part of the previous year's weeks)
and Calendar defines it as the docs state - so to change the value returned would mean you having to change the "FirstDayOfWeek" or the "MinimalDaysInFirstWeek" - which (without checking recently) I think the ISO standard also defines so you can't safely change these
I might raise a RFE against Calendar about this in a week or two since it seems quite important?
thanks,
asjf