日期转为本年第几周

private static String dateWeek(String datew) throws ParseException
{
  SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");
  Date date = format.parse(datew);
  Calendar calendar = Calendar.getInstance();
  calendar.setFirstDayOfWeek(Calendar.MONDAY);
  calendar.setTime(date);
  String Week= datew.substring(datew.length()-4,datew.length())+String.valueOf(calendar.get(Calendar.WEEK_OF_YEAR));
  return Week;
}