根據開始時間和周期計算結束時間（一個月，兩個月，三個月為周期）

String visitDate=hypertensionVisit.getVisitDate();
System.out.println(visitDate);
Calendar cal = Calendar.getInstance();
Date date = null;
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
try {
    date = sdf.parse(visitDate);
    System.out.println(date);
} catch (ParseException e) {
    e.printStackTrace();
}
cal.setTime(date);

String period = hypertensionVisit.getPeriod();

if ("3個月".equals(period)) {
    cal.add(Calendar.MONTH, 3);

}else if("2個月".equals(period)){
    cal.add(Calendar.MONTH, 2);
}
else {
    cal.add(Calendar.MONTH, 1);
}
Date date2 = cal.getTime();

String nextDate = sdf.format(date2);

String newNextDate = nextDate.replace(" ", "T");
hypertensionVisit.setNextDate(newNextDate);