Working with Dates in Kotlin: Libraries and Tools (Kotlinx-datetime, Joda-Time, java.time)

Working with Dates in Kotlin: Overview of Libraries and Tools

Date and time handling is one of the key tasks in any application: from event logging to calculating deadlines and displaying calendars. In Kotlin, as a language running on top of the JVM (and also supporting multiplatform projects), developers have access to several powerful libraries. In this article, we will look at three main approaches: kotlinx-datetime (recommended for multiplatform), java.time (for JVM/Android), and Joda-Time (a legendary library, relevant for legacy projects).

1. kotlinx-datetime — Official Multiplatform Library

kotlinx-datetime is a modern library from JetBrains, created specifically for Kotlin Multiplatform. It provides a unified API for working with dates, times, time zones, and durations on all platforms (JVM, JS, Native).

Installation (Gradle)

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

Main Classes and Examples

• Instant — a moment in time (UTC).
• LocalDateTime — date+time without a time zone.
• LocalDate — date only.
• LocalTime — time only.
• TimeZone — time zone.

import kotlinx.datetime.*

fun main() {    // Current moment in UTC    val now: Instant = Clock.System.now()    println("Now UTC: $now")

    // Conversion to local time (system time zone)    val localDateTime: LocalDateTime = now.toLocalDateTime(TimeZone.currentSystemDefault())    println("Local: $localDateTime")

    // Working with dates    val today: LocalDate = localDateTime.date    val tomorrow: LocalDate = today.plus(1, DateTimeUnit.DAY)    println("Tomorrow: $tomorrow")

    // Difference between dates    val daysBetween = tomorrow.daysUntil(today)    println("Days between: $daysBetween") // -1

    // Parsing a string    val parsedDate = LocalDate.parse("2025-03-15")    println("Parsed: $parsedDate")}

2. java.time (ThreeTen-Backport) — Standard for JVM and Android

Starting with Java 8, the java.time package (JSR-310) was included in the standard library. For Android API < 26, ThreeTen-Backport (or ThreeTenABP for Android) is used. Kotlin is fully compatible with this API.

Installation (for Android with minSdk < 26)

dependencies {    implementation("org.threeten:threetenbp:1.6.9")}

Examples

import java.time.*

fun main() {    // Current date and time    val now = LocalDateTime.now()    println("Now: $now")

    // Creating a specific date    val date = LocalDate.of(2025, Month.DECEMBER, 25)    println("Christmas: $date")

    // Formatting    val formatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm")    val formatted = now.format(formatter)    println("Formatted: $formatted")

    // Difference between dates    val start = LocalDate.of(2025, 1, 1)    val end = LocalDate.of(2025, 12, 31)    val days = ChronoUnit.DAYS.between(start, end)    println("Days in 2025: $days") // 364}

3. Joda-Time — A Time-Tested Library

Joda-Time was the de facto standard before java.time appeared. Today it is mainly used in legacy projects. The library provides rich functionality but is considered outdated — migration to java.time or kotlinx-datetime is recommended.

Installation

dependencies {    implementation("joda-time:joda-time:2.12.7")}

Example

import org.joda.time.*import org.joda.time.format.DateTimeFormat

fun main() {    val now = DateTime.now()    println("Now: $now")

    // Add