Working with Dates and Time in Kotlin: Advanced Techniques and API

Advanced Work with Dates and Time in Kotlin

In modern Kotlin development, working with dates and time goes far beyond simply displaying the current date. At an advanced level, it is necessary to consider time zones, perform complex calculations with periods, parse non-standard formats, and handle timestamps in distributed systems. In this article, we will look at the key libraries and techniques that will help you write reliable and efficient code for working with dates and time in Kotlin.

1. Choosing a Library: java.time vs kotlinx-datetime

Kotlin is fully compatible with Java, so you can use the powerful java.time API (JSR-310), which is the standard for new projects. However, for multiplatform projects (KMP), it is better to choose kotlinx-datetime from JetBrains.

java.time (JVM)

Main classes: LocalDate, LocalTime, LocalDateTime, ZonedDateTime, Instant, Duration, Period.

import java.time.*

fun main() {    val today = LocalDate.now()    val meetingTime = LocalDateTime.of(2025, 3, 15, 14, 30)    val zonedMeeting = ZonedDateTime.of(meetingTime, ZoneId.of("Europe/Moscow"))    println("Meeting in Moscow: $zonedMeeting")}

kotlinx-datetime (Multiplatform)

Add the dependency to build.gradle.kts:

implementation("org.jetbrains.kotlinx:kotlinx-datetime:0.6.1")

import kotlinx.datetime.*

fun main() {    val now = Clock.System.now()    val date = now.toLocalDateTime(TimeZone.of("Europe/Moscow")).date    println("Today: $date")}

2. Parsing and Formatting Dates

Correct parsing is the foundation of working with external data. Let's look at advanced techniques.

Parsing with Non-Standard Formats

import java.time.LocalDateTimeimport java.time.format.DateTimeFormatterimport java.time.format.DateTimeParseException

fun parseCustomDate(dateString: String): LocalDateTime? {    val formatters = listOf(        DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"),        DateTimeFormatter.ofPattern("dd/MM/yyyy'T'HH:mm"),        DateTimeFormatter.ISO_LOCAL_DATE_TIME    )    for (formatter in formatters) {        try {            return LocalDateTime.parse(dateString, formatter)        } catch (e: DateTimeParseException) {            // try the next one        }    }    return null}

fun main() {    println(parseCustomDate("2025-03-15 14:30:00")) // 2025-03-15T14:30    println(parseCustomDate("15/03/2025T14:30"))    // 2025-03-15T14:30}

Localized Formatting

import java.time.LocalDateimport java.time.format.DateTimeFormatterimport java.time.format.FormatStyleimport java.util.Locale

fun main() {    val date = LocalDate.of(2025, 3, 15)    val usFormatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL)        .withLocale(Locale.US)    val ruFormatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL)        .withLocale(Locale("ru"))    println("USA: ${date.format(usFormatter)}")  // Saturday, March 15, 2025    println("RU:  ${date.format(ruFormatter)}")  // суббота, 15 марта 2025 г.}

3. Complex Calculations with Duration and Period

Duration — for precise time intervals (hours, minutes, seconds), Period — for calendar periods (years, months, days).

Difference Between Dates Considering Business Logic

import java.time.*import java.time.temporal.ChronoUnit

fun businessDaysBetween(start: LocalDate, end: LocalDate): Long {    var count = 0L    var current = start    while (current.isBefore(end)) {        if (current.dayOfWeek != DayOfWeek.SATURDAY &&             current.dayOfWeek != DayOfWe