Kotlin Help


Plugin and versions

The kotlin-maven-plugin compiles Kotlin sources and modules. Currently, only Maven v3 is supported.

Define the version of Kotlin you want to use via a kotlin.version property:

<properties> <kotlin.version>1.8.10</kotlin.version> </properties>


Kotlin has an extensive standard library that can be used in your applications. To use the standard library in your project, add the following dependency in the pom file:

<dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-stdlib</artifactId> <version>${kotlin.version}</version> </dependency> </dependencies>

If your project uses Kotlin reflection or testing facilities, you need to add the corresponding dependencies as well. The artifact IDs are kotlin-reflect for the reflection library, and kotlin-test and kotlin-test-junit for the testing libraries.

Compile Kotlin-only source code

To compile source code, specify the source directories in the <build> tag:

<build> <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory> <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory> </build>

The Kotlin Maven Plugin needs to be referenced to compile the sources:

<build> <plugins> <plugin> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-maven-plugin</artifactId> <version>${kotlin.version}</version> <executions> <execution> <id>compile</id> <goals> <goal>compile</goal> </goals> </execution> <execution> <id>test-compile</id> <goals> <goal>test-compile</goal> </goals> </execution> </executions> </plugin> </plugins> </build>

Compile Kotlin and Java sources

To compile projects that include Kotlin and Java source code, invoke the Kotlin compiler before the Java compiler. In maven terms that means that kotlin-maven-plugin should be run before maven-compiler-plugin using the following method, making sure that the kotlin plugin comes before the maven-compiler-plugin in your pom.xml file:

<build> <plugins> <plugin> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-maven-plugin</artifactId> <version>${kotlin.version}</version> <executions> <execution> <id>compile</id> <goals> <goal>compile</goal> </goals> <configuration> <sourceDirs> <sourceDir>${project.basedir}/src/main/kotlin</sourceDir> <sourceDir>${project.basedir}/src/main/java</sourceDir> </sourceDirs> </configuration> </execution> <execution> <id>test-compile</id> <goals> <goal>test-compile</goal> </goals> <configuration> <sourceDirs> <sourceDir>${project.basedir}/src/test/kotlin</sourceDir> <sourceDir>${project.basedir}/src/test/java</sourceDir> </sourceDirs> </configuration> </execution> </executions> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.5.1</version> <executions> <!-- Replacing default-compile as it is treated specially by maven --> <execution> <id>default-compile</id> <phase>none</phase> </execution> <!-- Replacing default-testCompile as it is treated specially by maven --> <execution> <id>default-testCompile</id> <phase>none</phase> </execution> <execution> <id>java-compile</id> <phase>compile</phase> <goals> <goal>compile</goal> </goals> </execution> <execution> <id>java-test-compile</id> <phase>test-compile</phase> <goals> <goal>testCompile</goal> </goals> </execution> </executions> </plugin> </plugins> </build>

Incremental compilation

To make your builds faster, you can enable incremental compilation for Maven by defining the kotlin.compiler.incremental property:

<properties> <kotlin.compiler.incremental>true</kotlin.compiler.incremental> </properties>

Alternatively, run your build with the -Dkotlin.compiler.incremental=true option.

Annotation processing

See the description of Kotlin annotation processing tool (kapt).

Jar file

To create a small Jar file containing just the code from your module, include the following under build->plugins in your Maven pom.xml file, where main.class is defined as a property and points to the main Kotlin or Java class:

<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.6</version> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <mainClass>${main.class}</mainClass> </manifest> </archive> </configuration> </plugin>

Self-contained Jar file

To create a self-contained Jar file containing the code from your module along with dependencies, include the following under build->plugins in your Maven pom.xml file, where main.class is defined as a property and points to the main Kotlin or Java class:

<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-assembly-plugin</artifactId> <version>2.6</version> <executions> <execution> <id>make-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> <configuration> <archive> <manifest> <mainClass>${main.class}</mainClass> </manifest> </archive> <descriptorRefs> <descriptorRef>jar-with-dependencies</descriptorRef> </descriptorRefs> </configuration> </execution> </executions> </plugin>

This self-contained jar file can be passed directly to a JRE to run your application:

java -jar target/mymodule-0.0.1-SNAPSHOT-jar-with-dependencies.jar

Specifying compiler options

Additional options and arguments for the compiler can be specified as tags under the <configuration> element of the Maven plugin node:

<plugin> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-maven-plugin</artifactId> <version>${kotlin.version}</version> <executions>...</executions> <configuration> <nowarn>true</nowarn> <!-- Disable warnings --> <args> <arg>-Xjsr305=strict</arg> <!-- Enable strict mode for JSR-305 annotations --> ... </args> </configuration> </plugin>

Many of the options can also be configured through properties:

<project ...> <properties> <kotlin.compiler.languageVersion>1.0</kotlin.compiler.languageVersion> </properties> </project>

The following attributes are supported:

Attributes common to JVM and JS


Property name


Possible values

Default value


Generate no warnings

true, false




Provide source compatibility with the specified version of Kotlin

"1.4" (DEPRECATED), "1.5", "1.6", "1.7", "1.8", "1.9"



Allow using declarations only from the specified version of bundled libraries

"1.3" (DEPRECATED), "1.4" (DEPRECATED), "1.5", "1.6", "1.7", "1.8", "1.9"


The directories containing the source files to compile

The project source roots


Enabled compiler plugins



Options for compiler plugins



Additional compiler arguments


Attributes specific to JVM


Property name


Possible values

Default value



Target version of the generated JVM bytecode

"1.8", "9", "10", ..., "19"




Include a custom JDK from the specified location into the classpath instead of the default JAVA_HOME

Attributes specific to JS


Property name


Possible values

Default value


Destination *.js file for the compilation result


Generate .meta.js and .kjsm files with metadata. Use to create a library

true, false



Generate source map

true, false



Embed source files into source map

"never", "always", "inlining"



Add the specified prefix to paths in the source map


The kind of JS module generated by the compiler

"umd", "commonjs", "amd", "plain"


Using BOM

To use a Kotlin Bill of Materials (BOM), write a dependency on kotlin-bom:

<dependencyManagement> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-bom</artifactId> <version>1.8.10</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement>

Generating documentation

The standard Javadoc generation plugin (maven-javadoc-plugin) does not support Kotlin code. To generate documentation for Kotlin projects, use Dokka; please refer to the Dokka README for configuration instructions. Dokka supports mixed-language projects and can generate output in multiple formats, including standard Javadoc.


For OSGi support see the Kotlin OSGi page.

Last modified: 07 February 2023