code: public static Date getWeekDay(Date dt, int weekDay) {
          Calendar cal = new GregorianCalendar();
          cal.setTime(dt);
          if (weekDay == 7) {
              weekDay = 1;
          } else {
              weekDay++;
          }
          cal.set(GregorianCalendar.DAY_OF_WEEK, weekDay);
          return cal.getTime();
      }
docs: @param dt      Date 给定的java.util.Date对象
  @param weekDay int 就是周几的”几“，周日是7
  
  @return Date java.util.Date对象