日期獲取Calendar，獲取本週第一天，本月第一天，往前7天，往前30的日期

獲取每個月的第一天

	public static String getFirstDay(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        Date firstDayOfMonth = calendar.getTime();
        return simpleDateFormat.format(firstDayOfMonth);
    }

獲取每個月的最後一天

	public static String getLastDate(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        calendar.add(Calendar.MONTH, 1);//加一個月
        calendar.add(Calendar.DAY_OF_MONTH, -1);
        Date lastDayOfMonth = calendar.getTime();
        return simpleDateFormat.format(lastDayOfMonth);
    }

獲取每週的第一天

	public static String getFirstOfWeek(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_WEEK, 2);
        Date firstDayOfMonth = calendar.getTime();
        return simpleDateFormat.format(firstDayOfMonth);
    }

獲取每週的最後一天

	public static String getLastOfWeek(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_WEEK, 2);
        calendar.add(Calendar.WEEK_OF_MONTH,1);//加一週
        calendar.add(Calendar.DAY_OF_WEEK,-1);//在當前時間上減去天數
        Date firstDayOfMonth = calendar.getTime();
        return simpleDateFormat.format(firstDayOfMonth);
    }

獲取當前時間減去7天

	public static String before7Days(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.DAY_OF_MONTH, -7);//在當前時間上減去天數
        Date before7Days = calendar.getTime();
        return simpleDateFormat.format(before7Days);
    }

獲取當前時間減去30天

	public static String before30Days(Date date){
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.DAY_OF_MONTH, -30);//在當前時間上減去天數
        Date before7Days = calendar.getTime();
        return simpleDateFormat.format(before7Days);
    }