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kotlin-logging CI Slack channel Maven Central Apache License V.2

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

Call log methods, without checking whether the respective log level is enabled

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!")

Define the logger, without explicitly specifying the class name

// 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")

Log exceptions in a Kotlin-style

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

Fluent logging in a Kotlin-style

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

Getting started

import io.github.oshai.kotlinlogging.KotlinLogging

private val logger = KotlinLogging.logger {} 

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

Version 5 vs. previous versions

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:

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

Download

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.

Maven

<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.

Gradle

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

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

Multiplatform

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

Overview

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:

Who is using it

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

FAQ

Usage

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

Support

More links

Contributing

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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