JDK8 获取一个月的第一（最后）一天

/**
     * 获取一个月的最后一天
     * @return
     * @exception
     * @date       2019/5/17 10:35
     */
    public static String getLastDayOfMonth() {
        LocalDate today = LocalDate.now();
        LocalDate lastDay = today.with(TemporalAdjusters.lastDayOfMonth());
        LocalDateTime lastDayTime = localDateToLocalDateTime(lastDay);
        return localDateTime2YMDHMS(lastDayTime);
    }


  /**
     * LocalDate To LocalDateTime
     * @return
     * @exception
     * @date       2019/5/17 14:13
     */
    public static LocalDateTime localDateToLocalDateTime(LocalDate localDate) {

        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDate.atStartOfDay().atZone(zone).toInstant();
        Date date =  Date.from(instant);

        instant = date.toInstant();
        zone = ZoneId.systemDefault();
       return LocalDateTime.ofInstant(instant, zone);
    }

 /**
     * 获取一个月的第一天
     * @return
     * @exception
     * @date       2019/5/17 10:34
     */
    public static String getFirstDayOfMonth() {
        LocalDate today = LocalDate.now();
        LocalDate firstday = LocalDate.of(today.getYear(),today.getMonth(),1);
        LocalDateTime firstDayTime = localDateToLocalDateTime(firstday);
        return localDateTime2YMDHMS(firstDayTime);
    }


 /**
     * localDateTime2YMDHMS
     * 返回的格式为 yyyy-MM-dd HH:mm:ss
     *
     * @return
     * @throws
     * @date 2019/1/7 12:04
     */
    public static String localDateTime2YMDHMS(LocalDateTime localDateTime) {
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        return df.format(localDateTime);
    }