java根据日期获取周几和获取某段时间内周几的日期

整理两个日期的方法。

根据日期获取当天是周几

    /**
     * 根据日期获取当天是周几
     * @param datetime 日期
     * @return 周几
     */
    public static String dateToWeek(String datetime) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        String[] weekDays = {"星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"};
        Calendar cal = Calendar.getInstance();
        Date date;
        try {
            date = sdf.parse(datetime);
            cal.setTime(date);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        int w = cal.get(Calendar.DAY_OF_WEEK) - 1;
        return weekDays[w];
    }

获取某段时间内的周一（二等等）的日期

    /**
     * 获取某段时间内的周一（二等等）的日期
     * @param dataBegin 开始日期
     * @param dataEnd 结束日期
     * @param weekDays 获取周几，1－6代表周一到周六。0代表周日
     * @return 返回日期List
     */
    public static List<String> getDayOfWeekWithinDateInterval(String dataBegin, String dataEnd, int weekDays) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        List<String> dateResult = new ArrayList<>();
        Calendar cal = Calendar.getInstance();
        String[] dateInterval = {dataBegin, dataEnd};
        Date[] dates = new Date[dateInterval.length];
        for (int i = 0; i < dateInterval.length; i++) {
            String[] ymd = dateInterval[i].split("[^\\d]+");
            cal.set(Integer.parseInt(ymd[0]), Integer.parseInt(ymd[1]) - 1, Integer.parseInt(ymd[2]));
            dates[i] = cal.getTime();
        }
        for (Date date = dates[0]; date.compareTo(dates[1]) <= 0; ) {
            cal.setTime(date);
            cal.add(Calendar.DATE, 1);
            date = cal.getTime();
            if (cal.get(Calendar.DAY_OF_WEEK) - 1 == weekDays) {
                String format = sdf.format(date);
                dateResult.add(format);
            }
        }
        return dateResult;
    }