Logging for Kotlin: Best Solutions and Libraries

Logging for Kotlin: Best Solutions and Libraries

Logging is an integral part of developing any serious application. In the Kotlin ecosystem, which is actively used both for server-side development (Ktor, Spring Boot) and mobile applications (Android), choosing the right tool for recording logs is critically important for debugging, monitoring, and performance analysis. In this article, we will look at the best libraries and approaches to logging in Kotlin, their features, and usage examples.

Why is logging important in Kotlin?

Kotlin is a statically typed language running on top of the JVM (or Native/JS). This provides access to all mature Java solutions, but Kotlin also offers its own convenient wrappers. Properly configured logging allows you to:

• Track the execution flow and variable states;
• Record errors and exceptions with context;
• Analyze performance (time measurements);
• Collect data for security auditing.

Without logging, any problem in production turns into a "black box".

Top 5 Solutions for Logging in Kotlin

1. SLF4J + Logback — The Classic Standard

SLF4J (Simple Logging Facade for Java) is a facade, and Logback is the most popular implementation. This is the de facto standard for JVM projects. Kotlin works perfectly with it.

Example configuration in build.gradle.kts:

dependencies {    implementation("ch.qos.logback:logback-classic:1.4.14")    implementation("org.slf4j:slf4j-api:2.0.9")}

Usage in Kotlin code:

import org.slf4j.LoggerFactory

class OrderService {    private val log = LoggerFactory.getLogger(OrderService::class.java)

    fun processOrder(orderId: String) {        log.info("Processing order: {}", orderId)        try {            // business logic        } catch (e: Exception) {            log.error("Error processing order {}", orderId, e)        }    }}

Pros: maximum flexibility, support for asynchronous appenders, file rotation. Cons: requires manual XML/config setup.

2. Kotlin Logging (klogging) — A "Lightweight" Wrapper

The Kotlin Logging library (not to be confused with KLogging) is a thin wrapper over SLF4J that makes code cleaner thanks to extension functions and lambdas.

Setup:

dependencies {    implementation("io.github.microutils:kotlin-logging:3.0.5")}

Example:

import mu.KLogging

class PaymentService {    companion object : KLogging()

    fun pay(amount: Double) {        logger.debug { "Starting payment for amount $amount" }        // logic        logger.info { "Payment successful: $amount" }    }}

Feature: lambda expressions inside curly braces are evaluated only if the logging level is active. This improves performance.

3. Timber — For Android and Beyond

Timber is a legendary library by Jake Wharton, originally created for Android. It allows a "fire and forget" approach: no need to declare a logger in every class.

Setup for Android:

dependencies {    implementation("com.jakewharton.timber:timber:5.0.1")}

Initialization in Application:

class App : Application() {    override fun onCreate() {        super.onCreate()        if (BuildConfig.DEBUG) {            Timber.plant(Timber.DebugTree())        } else {            Timber.plant(CrashReportingTree())        }    }}

Usage everywhere:

Timber.d("User clicked button: %s", buttonId)Timber.e(exception, "Critical error")

Pros: minimalism, automatic