Maven

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>1.6.0</kotlin.version> </properties> 

Dependencies

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 you're targeting JDK 7 or JDK 8, you can use extended versions of the Kotlin standard library. They contain additional extension functions for APIs added in new JDK versions. Instead of kotlin-stdlib, use kotlin-stdlib-jdk7 or kotlin-stdlib-jdk8, depending on your JDK version.

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:

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.

OSGi

For OSGi support see the Kotlin OSGi page.