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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>1.1.51</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-jre7 or kotlin-stdlib-jre8, 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.

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>
            <artifactId>kotlin-maven-plugin</artifactId>
            <groupId>org.jetbrains.kotlin</groupId>
            <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 kotlin-maven-plugin should be run before maven-compiler-plugin using the following method, making sure that the kotlin plugin is above the maven-compiler-plugin in your pom.xml file:

<build>
    <plugins>
        <plugin>
            <artifactId>kotlin-maven-plugin</artifactId>
            <groupId>org.jetbrains.kotlin</groupId>
            <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 (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

Targeting JavaScript

In order to compile JavaScript code, you need to use the js and test-js goals for the compile execution:

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

You also need to change the standard library dependency:

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

For unit testing support, you also need to add a dependency on the kotlin-test-js artifact.

See the Getting Started with Kotlin and JavaScript with Maven tutorial for more information.

Specifying compiler options

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

<plugin>
    <artifactId>kotlin-maven-plugin</artifactId>
    <groupId>org.jetbrains.kotlin</groupId>
    <version>${kotlin.version}</version>
    <executions>...</executions>
    <configuration>
        <nowarn>true</nowarn>  <!-- Disable warnings -->
    </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 specified language version "1.0", "1.1" "1.1"
apiVersion kotlin.compiler.apiVersion Allow to use declarations only from the specified version of bundled libraries "1.0", "1.1" "1.1"
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" "1.6"
jdkHome kotlin.compiler.jdkHome Path to JDK home directory to include into classpath, if differs from default JAVA_HOME    

Attributes specific for JS

Name Property name Description Possible values Default value
outputFile   Output file path    
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   Prefix for paths in a source map    
moduleKind   Kind of a module generated by compiler "plain", "amd", "commonjs", "umd" "plain"

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