DateTime.java

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
java.util.Date date = new java.util.Date();
String today = dateFormat.format(date);

Calendar calendar = Calendar.getInstance();
// set the calendar time (here, we set it to "today" / "now" date)
calendar.setTime(date);
calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY); // first day of week.
String firstDayInWeek = dateFormat.format(calendar.getTime());