java简单实现生日计算方法

/**
 * 获取日期月日的时间差
 *
 * @param date
 *
 * @param dateStr 格式YYYY-MM-dd
 *
 * @return 时间差单位(天)
 */
public static Integer getDateTimeBetween(Date date,String dateStr){
    if(Objects.isNull(date) || StringUtils.isBlank(dateStr)){
        return null;
    }

    DateFormat df = new SimpleDateFormat("yyyy");
    String currentYear = df.format(date);
    String birthDay = currentYear + dateStr.substring(4)+" 00:00:00";
    LocalDateTime localDateBirthDay = LocalDateTime.parse(birthDay, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

    Instant instant = date.toInstant();
    ZoneId zoneId = ZoneId.systemDefault();
    LocalDateTime currentDateTime = instant.atZone(zoneId).toLocalDateTime().withHour(0).withMinute(0).withSecond(0).withNano(0);

    Duration duration = Duration.between(localDateBirthDay, currentDateTime);
    return (int)duration.toDays();
}