如何在Kotlin中计算两个LocalDateTime的差值（非Java方式且微优化）

方法1：使用kotlinx.datetime内置until方法 #

kotlinx.datetime的LocalDateTime原生提供了until方法，无需依赖Java API，也不会转换为Instant（源码基于日期时间字段直接计算），完全符合你的微优化需求。

该方法支持按指定时间单位计算差值，可直接获取总秒数，也能拆分成年、月、日等单位的差值：

import kotlinx.datetime.LocalDateTime
import kotlinx.datetime.Month
import kotlinx.datetime.DateTimeUnit

fun main() {
    val startDate = LocalDateTime(year = 2020, month = Month.MARCH, dayOfMonth = 25, hour = 10, minute = 36, second = 12)
    val endDate = LocalDateTime(year = 2023, month = Month.FEBRUARY, dayOfMonth = 28, hour = 0, minute = 0, second = 1)

    // 计算总秒数差值
    val totalSeconds = startDate.until(endDate, DateTimeUnit.SECOND)
    println("总秒数差值: $totalSeconds")

    // 拆分多单位差值
    val years = startDate.until(endDate, DateTimeUnit.YEAR)
    val remainingAfterYears = startDate.plus(years, DateTimeUnit.YEAR)
    val months = remainingAfterYears.until(endDate, DateTimeUnit.MONTH)
    val remainingAfterMonths = remainingAfterYears.plus(months, DateTimeUnit.MONTH)
    val days = remainingAfterMonths.until(endDate, DateTimeUnit.DAY)
    val remainingAfterDays = remainingAfterMonths.plus(days, DateTimeUnit.DAY)
    val hours = remainingAfterDays.until(endDate, DateTimeUnit.HOUR)
    val remainingAfterHours = remainingAfterDays.plus(hours, DateTimeUnit.HOUR)
    val minutes = remainingAfterHours.until(endDate, DateTimeUnit.MINUTE)
    val seconds = remainingAfterHours.plus(minutes, DateTimeUnit.MINUTE).until(endDate, DateTimeUnit.SECOND)

    println("差值: $years 年, $months 月, $days 天, $hours 小时, $minutes 分钟, $seconds 秒")
}

注意：由于LocalDateTime不含时区信息，该计算基于公历字段差值，不会处理夏令时等时区相关调整，若无需此类修正可放心使用。

方法2：手动计算差值（极致性能优化） #

如果需要更极致的性能，可手动处理日期时间字段的差值与借位逻辑，完全无依赖：

import kotlinx.datetime.LocalDateTime
import kotlinx.datetime.Month

// 辅助函数：获取指定月份的天数（支持闰年判断）
fun getDaysInMonth(year: Int, month: Month): Int {
    return when (month) {
        Month.APRIL, Month.JUNE, Month.SEPTEMBER, Month.NOVEMBER -> 30
        Month.FEBRUARY -> if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) 29 else 28
        else -> 31
    }
}

fun calculateDateTimeDiff(start: LocalDateTime, end: LocalDateTime): Pair<Long, String> {
    var years = end.year - start.year
    var months = end.month.value - start.month.value
    var days = end.dayOfMonth - start.dayOfMonth
    var hours = end.hour - start.hour
    var minutes = end.minute - start.minute
    var seconds = end.second - start.second

    // 处理秒借位
    if (seconds < 0) {
        seconds += 60
        minutes -= 1
    }
    // 处理分钟借位
    if (minutes < 0) {
        minutes += 60
        hours -= 1
    }
    // 处理小时借位
    if (hours < 0) {
        hours += 24
        days -= 1
    }
    // 处理天数借位
    if (days < 0) {
        months -= 1
        val adjustedMonth = if (months < 0) Month.from(start.month.value + 11) else Month.from(start.month.value + months)
        days += getDaysInMonth(start.year + years, adjustedMonth)
    }
    // 处理月份借位
    if (months < 0) {
        months += 12
        years -= 1
    }

    // 计算精确总秒数（累加每个月实际天数）
    var totalDays = 0L
    var currentYear = start.year
    var currentMonth = start.month.value
    while (currentYear < end.year || (currentYear == end.year && currentMonth < end.month.value)) {
        totalDays += getDaysInMonth(currentYear, Month.from(currentMonth)).toLong()
        currentMonth += 1
        if (currentMonth > 12) {
            currentMonth = 1
            currentYear += 1
        }
    }
    totalDays += end.dayOfMonth - start.dayOfMonth
    // 处理天数借位后的调整
    if (end.dayOfMonth < start.dayOfMonth) {
        totalDays -= getDaysInMonth(start.year, start.month).toLong()
        totalDays += getDaysInMonth(end.year, end.month).toLong()
    }

    val totalSeconds = totalDays * 24 * 3600 + hours * 3600L + minutes * 60L + seconds
    val diffStr = "$years 年, $months 月, ${totalDays % 365} 天, $hours 小时, $minutes 分钟, $seconds 秒"

    return Pair(totalSeconds, diffStr)
}

fun main() {
    val startDate = LocalDateTime(year = 2020, month = Month.MARCH, dayOfMonth = 25, hour = 10, minute = 36, second = 12)
    val endDate = LocalDateTime(year = 2023, month = Month.FEBRUARY, dayOfMonth = 28, hour = 0, minute = 0, second = 1)

    val (totalSeconds, diffStr) = calculateDateTimeDiff(startDate, endDate)
    println("总秒数差值: $totalSeconds")
    println("详细差值: $diffStr")
}

该方法完全规避了任何外部方法调用，性能达到最优，适合严格的微优化场景。

内容的提问来源于stack exchange，提问作者MohammadBaqer