public static Calendar toCalendar(String date) throws IOException 
{
        Calendar retval = null;
        if( date != null && date.trim().length()  > 0 )
        {
            //these are the default values
            int year = 0;
            int month = 1;
            int day = 1;
            int hour = 0;
            int minute = 0;
            int second = 0;
            //first string off the prefix if it exists
            try
            {
                SimpleTimeZone zone = null;
                if( date.startsWith( "D:" ) )
                {
                    date = date.substring( 2, date.length() );
                }
                date = date.replaceAll("[-:T]", "");
                if( date.length() <  4 )
                {
                    throw new IOException( "Error: Invalid date format '" + date + "'" );
                }
                year = Integer.parseInt( date.substring( 0, 4 ) );
                if( date.length()  >= 6 )
                {
                    month = Integer.parseInt( date.substring( 4, 6 ) );
                }
                if( date.length()  >= 8 )
                {
                    day = Integer.parseInt( date.substring( 6, 8 ) );
                }
                if( date.length()  >= 10 )
                {
                    hour = Integer.parseInt( date.substring( 8, 10 ) );
                }
                if( date.length()  >= 12 )
                {
                    minute = Integer.parseInt( date.substring( 10, 12 ) );
                }
                if( date.length()  >= 14 )
                {
                    second = Integer.parseInt( date.substring( 12, 14 ) );
                }
                if( date.length()  >= 15 )
                {
                    char sign = date.charAt( 14 );
                    if( sign == 'Z' )
                    {
                        zone = new SimpleTimeZone(0,"Unknown");
                    }
                    else
                    {
                        int hours = 0;
                        int minutes = 0;
                        if( date.length()  >= 17 )
                        {
                            if( sign == '+' )
                            {
                                //parseInt cannot handle the + sign
                                hours = Integer.parseInt( date.substring( 15, 17 ) );
                            }
                            else
                            {
                                hours = -Integer.parseInt( date.substring( 14, 16 ) );
                            }
                        }
                        if( sign=='+' )
                        {
                            if( date.length()  >= 19 )
                            {
                                minutes = Integer.parseInt( date.substring( 17, 19 ) );
                            }
                        }
                        else
                        {
                            if( date.length()  >= 18 )
                            {
                                minutes = Integer.parseInt( date.substring( 16, 18 ) );
                            }
                        }
                        zone = new SimpleTimeZone( hours*60*60*1000 + minutes*60*1000, "Unknown" );
                    }
                }
                if( zone == null )
                {
                    retval = new GregorianCalendar();
                }
                else
                {
                    retval = new GregorianCalendar( zone );
                }
                retval.clear();
                retval.set( year, month-1, day, hour, minute, second );
            }
            catch( NumberFormatException e )
            {
                // remove the arbitrary : in the timezone. SimpleDateFormat
                // can't handle it           
                if (date.substring(date.length()-3,date.length()-2).equals(":") &&
                        (date.substring(date.length()-6,date.length()-5).equals("+") ||
                                date.substring(date.length()-6,date.length()-5).equals("-"))) 
                {
                    //thats a timezone string, remove the :
                    date = date.substring(0,date.length()-3) + 
                           date.substring(date.length()-2);
                }
                for( int i=0; retval == null && i< POTENTIAL_FORMATS.length; i++ )
                {
                    try
                    {
                        Date utilDate = POTENTIAL_FORMATS[i].parse( date ); 
                        retval = new GregorianCalendar();
                        retval.setTime( utilDate );
                    }
                    catch( ParseException pe )
                    {
                        //ignore and move to next potential format
                    }
                }
                if( retval == null )
                {
                    //we didn't find a valid date format so throw an exception
                    throw new IOException( "Error converting date:" + date );
                }
            }
        }
        return retval;
}

This will convert a string to a calendar.

 public static String toISO8601(Calendar cal) 
{
        StringBuffer retval = new StringBuffer();
        retval.append( cal.get( Calendar.YEAR ) );
        retval.append( "-" );
        zeroAppend( retval, cal.get( Calendar.MONTH )+1 );
        retval.append( "-" );
        zeroAppend( retval, cal.get( Calendar.DAY_OF_MONTH ) );
        retval.append( "T" );
        zeroAppend( retval, cal.get( Calendar.HOUR_OF_DAY ));
        retval.append( ":" );
        zeroAppend( retval, cal.get( Calendar.MINUTE ));
        retval.append( ":" );
        zeroAppend( retval, cal.get( Calendar.SECOND ));
        int timeZone = cal.get( Calendar.ZONE_OFFSET ) + cal.get(Calendar.DST_OFFSET );
        if( timeZone <  0 )
        {
            retval.append( "-" );
        }
        else
        {
            retval.append( "+" );
        }
        timeZone = Math.abs( timeZone );
        //milliseconds/1000 = seconds = seconds / 60 = minutes = minutes/60 = hours
        int hours = timeZone/1000/60/60;
        int minutes = (timeZone - (hours*1000*60*60))/1000/1000;
        if( hours <  10 )
        {
            retval.append( "0" );
        }
        retval.append( Integer.toString( hours ) );
        retval.append( ":" );
        if( minutes <  10 )
        {
            retval.append( "0" );
        }
        retval.append( Integer.toString( minutes ) );
        return retval.toString();
}

Convert the date to iso 8601 string format.