【工具类】获取月份的第一天

获取月份的第一天

	// 传入YYYY-MM
    public static String toFirstDayOfMonth(String yearMonth) {
        YearMonth ym = YearMonth.parse(yearMonth, DateTimeFormatter.ofPattern("yyyy-MM"));
        LocalDate firstDay = ym.atDay(1);
        //返回YYYY-MM-01
        return firstDay.toString();
    }