Lightweight Multiplatform logging framework for Kotlin, written in .
A convenient and performant logging facade.

logger.debug { "Some $expensive message!" }

Behind the scenes the expensive message do not get evaluated if debug is not enabled:

// This is what happens when you write the above ^^^
if (logger.isDebugEnabled) logger.debug("Some $expensive message!")

// Place definition above class declaration to make field static
private val logger = KotlinLogging.logger {}

Behind the scenes val logger will be created in the class, with the class/file name:

// This is what happens when you write the above ^^^
val logger = LoggerFactory.getLogger("package.ClassName")

// exception as first parameter with message as lambda
logger.error(exception) { "a $fancy message about the $exception" }

logger.atWarn {
    message    = "foo $bar"
    cause      = exception
    payload    = buildMap(capacity = 3) {
        put("foo", 1)
        put("bar", "x")
        put("obj", Pair(2, 3))
    }
}

import io.github.oshai.kotlinlogging.KotlinLogging

private val logger = KotlinLogging.logger {} 

class FooWithLogging {
    val message = "world"
    fun bar() {
        logger.debug { "hello $message" }
    }
}

Version 5 is not backward compatible with previous versions (v.3, v.2, v.1). Group id (in maven) and packages names changed. It is possible to use both version 5 and previous versions side-by-side so some of the code from the old version and some new. It is also possible to have libs using old version and use the new version (and vice-versa).
In that sense it's a completely new dependency.

Main changes are:

• Maven group id changed from io.github.microutils -> io.github.oshai.
• Root package change from mu -> io.github.oshai.kotlinlogging.
• Slf4j dependency is not provided anymore (users have to provide it). It means that >= 5.x can work with both slf4j 1 or 2.
• There are changes to multiplatform class hierarchy that might break compatibility.

More details in issue #264, and in the change log

Important note: kotlin-logging depends on slf4j-api (in the JVM artifact). In runtime, it is also required to depend on a logging implementation. More details in how-to-configure-slf4j. And an excellent detailed explanation in a-guide-to-logging-in-java.
In version 5 users should also provide slf4j-api dependency.

In short, if you just want to log statements to stdout, it's possible to add the following dependency: org.slf4j:slf4j-simple:2.0.3.

<dependency>
  <groupId>io.github.oshai</groupId>
  <artifactId>kotlin-logging-jvm</artifactId>
  <version>7.0.0</version>
</dependency>

See the full example in kotlin-logging-example-maven.

implementation 'io.github.oshai:kotlin-logging-jvm:7.0.0'

Alternatively, download the JAR from github or maven-central.

An experimental multiplatform support is available.
More information is available on the wiki and issues #21 #45.

After seeing many questions like Idiomatic way of logging in Kotlin and Best practices for loggers, it seems like there should be a standard for logging and obtaining a logger in Kotlin. kotlin-logging provides a wrapper for slf4j-api to be used by Kotlin classes with the following advantages:

• No need to write the logger and class name or logger name boilerplate code.
• A straight forward way to log messages with lazy-evaluated string using lambda expression {}.
• All previous slf4j implementation can still be used.

• https://www.jetbrains.com/youtrack/ (https://www.jetbrains.com/help/youtrack/standalone/Third-Party-Software-Used-by-YouTrack.html)
• https://github.com/DiUS/pact-jvm
• https://github.com/AsynkronIT/protoactor-kotlin
• https://github.com/square/misk
• https://github.com/openrndr/openrndr
• https://github.com/JetBrains/xodus

And many more... (add your name above)

• Why not use plain slf4j? kotlin-logging has better native Kotlin support. It adds more functionality and enables less boilerplate code.
• Is all slf4j implementation supported (Markers, params, etc')? Yes.
• Is location logging possible? Yes, location awareness was added in kotlin-logging 1.4.
• When I do logger.debug, my IntelliJ IDEA run console doesn't show any output. Do you know how I could set the console logger to debug or trace levels? Is this an IDE setting, or can it be set in the call to KLogging()? Setting log level is done per implementation. kotlin-logging and slf4j are just facades for the underlying logging lib (log4j, logback etc') more details here.
• Can I access the actual logger? In platforms available yes, via DelegatingKLogger.underlyingLogger property.

• See wiki for more examples.

It is possible to configure IntelliJ live templates. For file level logger configure the following:

• Text template: private val logger = io.github.oshai.kotlinlogging.KotlinLogging.logger {}.
• Applicable in Kotlin: top-level.

• Open an issue here: https://github.com/oshai/kotlin-logging/issues
• Ask a question in StackOverflow with kotlin-logging tag.
• Chat on Slack channel: https://kotlinlang.slack.com/messages/kotlin-logging
• Chat on Telegram channel: https://t.me/klogging

• https://medium.com/@OhadShai/logging-in-kotlin-95a4e76388f2
• kotlin-logging vs AnkoLogger for Android
• How kotlin-logging was published
• Kotlin Logging Without the Fuss
• DropWizard + Kotlin = Project Kronslott
• Logging in Kotlin – the right approach
• https://bednarek.wroclaw.pl/log4j-in-kotlin/
• https://jaxenter.com/kotlin-logging-168814.html

Any contribution is appreciated.
See the contributors list in: https://github.com/oshai/kotlin-logging/graphs/contributors

Pull requests are welcome! See instructions in https://github.com/oshai/kotlin-logging/blob/master/CONTRIBUTING.md.

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