I'm trying to compile maven project which has Kotlin classes referencing Java classes. Here's a part of my parent POM:
...
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib</artifactId>
<version>${kotlin.version}</version>
</dependency>
...
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${compiler-plugin-version}</version>
<configuration>
<source>${java-version}</source>
<target>${java-version}</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
</plugin>
<plugin>
<artifactId>kotlin-maven-plugin</artifactId>
<groupId>org.jetbrains.kotlin</groupId>
<version>${kotlin.plugin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>process-sources</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>test-compile</id>
<phase>process-test-sources</phase>
<goals>
<goal>test-compile</goal>
</goals>
</execution>
</executions>
<configuration>
<scanForAnnotations>false</scanForAnnotations>
</configuration>
</plugin>
And related parts of the child POM:
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib</artifactId>
</dependency>
...
<plugin>
<artifactId>kotlin-maven-plugin</artifactId>
<groupId>org.jetbrains.kotlin</groupId>
<configuration>
<sourceDirs>
<source>${project.basedir}/src/main/kotlin</source>
</sourceDirs>
</configuration>
</plugin>
And the Kotlin class:
Stateless
open class DummyServiceImpl : DummyService {
PersistenceContext(unitName = Consts.UNIT_NAME)
private val em: EntityManager? = null
override fun get(id: Long?): Dummy {
return em!!.find<Dummy>(javaClass<Dummy>(), id)
}
override fun sayHi(): String {
return "Dummy service says \"Hi!\"."
}
}
DummyService and Consts classes are Java classes residing in the same module as DummyServiceImpl.
So when I compile the module containing DummyServiceImpl with Maven it goes like this:
[error] C:\somepath\service\DummyServiceImpl.kt: (14, 31) Unresolved reference: DummyService
[error] C:\somepath\service\DummyServiceImpl.kt: (16, 35) Unresolved reference: Consts
If I switch Kotlin plugin execution phase to compile then it predictably fails if there're references from Java to Kotlin classes:
[ERROR] /C:/somepath/service/impl/DummyServiceClientImpl.java:[5,27] cannot find symbol
[ERROR] symbol: class DummyServiceImpl
So, what's to be done about this? Note that building with IDEA's make goes perfectly fine.
Make sure you have this declaration in <build> of your pom.xml
<plugins>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>process-sources</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/main/java</source>
<source>src/main/kotlin</source>
<source>src/main/resources</source>
</sourceDirs>
</configuration>
</execution>
<execution>
<id>test-compile</id>
<phase>process-test-sources</phase>
<goals>
<goal>test-compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/test/java</source>
<source>src/test/kotlin</source>
<source>src/test/resources</source>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
Make sure that all folders (3x in src/main & 3x in src/test) mentioned in the configuration actually exist, even if they don’t contain any classes/resources. You can still fine-tune the configuration once it works for you.
Also pay attention to use exactly the same order I mentioned above to let the compiler compile the Java code first.
Referred from this Kotlin + java demo apps
You have to execute mvn kotlin:compile before mvn package. mvn kotlin:compile will compile the Kotlin files to class files.
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.wffweb</groupId>
<artifactId>kotlinminimalproductionsample</artifactId>
<version>0.0.1</version>
<packaging>war</packaging>
<!--
To package as war:- mvn clean kotlin:compile package
-->
<properties>
<maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
<kotlin.version>1.2.21</kotlin.version>
</properties>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.websocket</groupId>
<artifactId>javax.websocket-api</artifactId>
<version>1.1</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.webfirmframework</groupId>
<artifactId>wffweb</artifactId>
<version>RELEASE</version>
</dependency>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib-jdk8</artifactId>
<version>${kotlin.version}</version>
</dependency>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-test</artifactId>
<version>${kotlin.version}</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
</includes>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.4.0</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>test-compile</goal>
</goals>
</execution>
</executions>
<configuration>
<jvmTarget>1.8</jvmTarget>
</configuration>
</plugin>
</plugins>
</build>
</project>
I ended using the following configuration to mix Java and Kotlin source code:
<build>
<sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
<testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
<plugins>
<plugin>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-maven-plugin</artifactId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/main/kotlin</source>
</sourceDirs>
</configuration>
</execution>
<execution>
<id>test-compile</id>
<phase>test-compile</phase>
<goals>
<goal>test-compile</goal>
</goals>
<configuration>
<sourceDirs>
<source>src/test/kotlin</source>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
