/* ISO 8601 date manipulation in Java 1.2.
   This was sent to me by Simon Brooke <simon@jasmine.org.uk>
   2000-11-22T15:20:52Z for inclusion into my material on ISO 8601.
   I don't understand much of it, but I include it in the hope
   that some people might find it useful. 
     Jukka K. Korpela, jkorpela@cs.tut.fi 
*/

public class Calendar extends GregorianCalendar
{
   /** Return an ISO8601 string representing the date/time
    *  represented by this Calendar */
   public String toString()
   {
   String timef = "'T'hh:mm:ss";
   String datef = "yyyy-MM-dd";
   String bothf = "yyyy-MM-dd'T'hh:mm:ss";
   boolean dotimezone = true;

   String format = bothf;    // initially assume this is a date/time

   if ( ( isSet( DAY_OF_MONTH) == false || get( DAY_OF_MONTH) == 1) &&
        ( isSet( MONTH) == false || get( MONTH) == 0) &&
        ( isSet( YEAR) == false || get( YEAR) == 1970))
               // it's highly probable that we're
               // looking at a time-of-day.
       format = timef;
   else
       if ( ( isSet( HOUR) == false || get( HOUR) == 0) &&
        ( isSet( MINUTE) == false || get( MINUTE) == 0) &&
        ( isSet( SECOND) == false || get( SECOND) == 0))
               // it's highly probable that we're
               // looking at a date.
       {
           format = datef;
           dotimezone = false;
       }

   DateFormat df = new SimpleDateFormat( format);
   StringBuffer result = new StringBuffer( df.format( getTime()));

   if ( dotimezone)    // we don't need to worry about timezone in
       {             // date only strings but otherwise we do...

       int offset = get( java.util.Calendar.ZONE_OFFSET);

       if ( offset == 0)
           result.append( "Z");
               // zero offset -- excellent, easy.
       else
           {        // horrible, horrible, oh most horrible.
           NumberFormat nf = new DecimalFormat( "00");

           offset = offset / 60000;
           int om = Math.abs( offset % 60),
               oh = Math.abs( offset / 60);
           String os = "+";

           if ( offset < 0) os = "-";

           result.append( os).append( nf.format( oh));

           if ( om > 0)
               result.append( nf.format( om));
           }
       }

   return result.toString();
   }
}