Date class helper

DateUtil.kt

import org.junit.Test
import java.time.DayOfWeek
import java.time.LocalDateTime
import java.time.LocalTime
import java.time.ZoneId
import java.time.format.DateTimeFormatter
import java.time.temporal.TemporalAdjusters
import java.util.*

class DateUtil {
    @Test
    fun test() {
        //day
        val now = LocalDateTime.now()
        println("Now: " + toString(now) + ", in mills: " + toMills(now))
        println("Start of day: " + toString(startOfDay()))
        println("End of day: " + toString(endOfDay()))
        println("Does '" + toString(now) + "' belong to the current day? > " + belongsToCurrentDay(now))
        val yesterday = now.minusDays(1)
        println("Does '" + toString(yesterday) + "' belong to the current day? > " + belongsToCurrentDay(yesterday))
        val tomorrow = now.plusDays(1)
        println("Does '" + toString(tomorrow) + "' belong to the current day? > " + belongsToCurrentDay(tomorrow))
        //week
        println("Start of week: " + toString(startOfWeek()))
        println("End of week: " + toString(endOfWeek()))
        println("Does '" + toString(now) + "' belong to the current week? > " + belongsToCurrentWeek(now))
        val previousWeek = now.minusWeeks(1)
        println("Does '" + toString(previousWeek) + "' belong to the current week? > " + belongsToCurrentWeek(previousWeek))
        val nextWeek = now.plusWeeks(1)
        println("Does '" + toString(nextWeek) + "' belong to the current week? > " + belongsToCurrentWeek(nextWeek))
        //month
        println("Start of month: " + toString(startOfMonth()))
        println("End of month: " + toString(endOfMonth()))
        println("Does '" + toString(now) + "' belong to the current month? > " + belongsToCurrentMonth(now))
        val previousMonth = now.minusMonths(1)
        println("Does '" + toString(previousMonth) + "' belong to the current month? > " + belongsToCurrentMonth(previousMonth))
        val nextMonth = now.plusMonths(1)
        println("Does '" + toString(nextMonth) + "' belong to the current month? > " + belongsToCurrentMonth(nextMonth))
    }

    companion object {
        private val DEFAULT_ZONE_ID = ZoneId.of("UTC")
        fun startOfDay(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MIN)
        }

        fun endOfDay(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MAX)
        }

        fun belongsToCurrentDay(localDateTime: LocalDateTime): Boolean {
            return localDateTime.isAfter(startOfDay()) && localDateTime.isBefore(endOfDay())
        }

        //note that week starts with Monday
        fun startOfWeek(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MIN)
                .with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY))
        }

        //note that week ends with Sunday
        fun endOfWeek(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MAX)
                .with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY))
        }

        fun belongsToCurrentWeek(localDateTime: LocalDateTime): Boolean {
            return localDateTime.isAfter(startOfWeek()) && localDateTime.isBefore(endOfWeek())
        }

        fun startOfMonth(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MIN)
                .with(TemporalAdjusters.firstDayOfMonth())
        }

        fun endOfMonth(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MAX)
                .with(TemporalAdjusters.lastDayOfMonth())
        }

        fun belongsToCurrentMonth(localDateTime: LocalDateTime): Boolean {
            return localDateTime.isAfter(startOfMonth()) && localDateTime.isBefore(endOfMonth())
        }

        fun startOfYear(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MIN)
                .with(TemporalAdjusters.firstDayOfYear())
        }

        fun endOfYear(): LocalDateTime {
            return LocalDateTime.now(DEFAULT_ZONE_ID)
                .with(LocalTime.MAX)
                .with(TemporalAdjusters.lastDayOfYear())
        }

        fun belongsToCurrentYear(localDateTime: LocalDateTime): Boolean {
            return localDateTime.isAfter(startOfYear()) && localDateTime.isBefore(endOfYear())
        }

        fun toMills(localDateTime: LocalDateTime): Long {
            return localDateTime.atZone(DEFAULT_ZONE_ID).toInstant().toEpochMilli()
        }

        fun toDate(localDateTime: LocalDateTime): Date {
            return Date.from(localDateTime.atZone(DEFAULT_ZONE_ID).toInstant())
        }

        fun toString(localDateTime: LocalDateTime): String {
            return localDateTime.format(DateTimeFormatter.ISO_DATE_TIME)
        }
    }
}

founded on stackoverflow, i forget the source