Using 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>1.4.21</kotlin.version>
</properties>
Dependencies
Kotlin has an extensive standard library that can be used in your applications. Configure the following dependency in the pom file:
<dependencies>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib</artifactId>
<version>${kotlin.version}</version>
</dependency>
</dependencies>
If you’re targeting JDK 7 or JDK 8, you can use extended versions of the Kotlin standard library which contain additional extension functions for APIs added in new JDK versions. Instead of kotlin-stdlib
, use kotlin-stdlib-jdk7
or kotlin-stdlib-jdk8
, depending on your JDK version (for Kotlin 1.1.x use kotlin-stdlib-jre7
and kotlin-stdlib-jre8
as the jdk
counterparts were introduced in 1.2.0).
If your project uses Kotlin reflection or testing facilities, you need to add the corresponding dependencies as well. The artifact IDs are kotlin-reflect
for the reflection library, and kotlin-test
and kotlin-test-junit
for the testing libraries.
Compiling Kotlin only source code
To compile source code, specify the source directories in the tag:
<build>
<sourceDirectory>${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>
Compiling Kotlin and Java sources
To compile mixed code applications Kotlin compiler should be invoked before Java compiler. In maven terms that means that kotlin-maven-plugin
should run before maven-compiler-plugin
using the following method. Make 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>${project.basedir}/src/test/java</sourceDir>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<executions>
<!-- Replacing default-compile as it is treated specially by maven -->
<execution>
<id>default-compile</id>
<phase>none</phase>
</execution>
<!-- Replacing default-testCompile as it is treated specially by maven -->
<execution>
<id>default-testCompile</id>
<phase>none</phase>
</execution>
<execution>
<id>java-compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>java-test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>testCompile</goal>
</goals>
<configuration>
<skip>${maven.test.skip}</skip>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
Incremental compilation
To make your builds faster, you can enable incremental compilation for Maven (supported since Kotlin 1.1.2). In order to do that, define 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 for JVM and JS
Name | Property name | Description | Possible values | Default value |
---|---|---|---|---|
nowarn | Generate no warnings | true, false | false | |
languageVersion | kotlin.compiler.languageVersion | Provide source compatibility with the specified version of Kotlin | “1.2 (DEPRECATED)”, “1.3”, “1.4”, “1.5 (EXPERIMENTAL)” | |
apiVersion | kotlin.compiler.apiVersion | Allow using declarations only from the specified version of bundled libraries | “1.2 (DEPRECATED)”, “1.3”, “1.4”, “1.5 (EXPERIMENTAL)” | |
sourceDirs | The directories containing the source files to compile | The project source roots | ||
compilerPlugins | Enabled compiler plugins | [] | ||
pluginOptions | Options for compiler plugins | [] | ||
args | Additional compiler arguments | [] |
Attributes specific for JVM
Name | Property name | Description | Possible values | Default value |
---|---|---|---|---|
jvmTarget | kotlin.compiler.jvmTarget | Target version of the generated JVM bytecode | “1.6”, “1.8”, “9”, “10”, “11”, “12”, “13”, “14”, “15” | “1.6” |
jdkHome | kotlin.compiler.jdkHome | Include a custom JDK from the specified location into the classpath instead of the default JAVA_HOME |
Attributes specific for JS
Name | Property name | Description | Possible values | Default value |
---|---|---|---|---|
outputFile | Destination *.js file for the compilation result | |||
metaInfo | Generate .meta.js and .kjsm files with metadata. Use to create a library | true, false | true | |
sourceMap | Generate source map | true, false | false | |
sourceMapEmbedSources | Embed source files into source map | “never”, “always”, “inlining” | “inlining” | |
sourceMapPrefix | Add the specified prefix to paths in the source map | |||
moduleKind | The kind of JS module generated by the compiler | “umd”, “commonjs”, “amd”, “plain” | “umd” |
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.
Examples
An example Maven project can be downloaded directly from the GitHub repository