java 獲取上周、本周、下周指定周幾的時間

Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, weekFlag * 7);
// 周日的時間
cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
String beginDateStr = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(cal.getTime());
// 周六的時間
cal.set(Calendar.DAY_OF_WEEK, Calendar.SATURDAY);
String endDateStr = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(cal.getTime());