When starting a new Java project recently, I found it surprisingly difficult to setup the Gradle build with support for Java 9 modules and the Kotlin language.
For others who might find themselves in the same bind, here is a gist with the simplest, minimal gradle setup I came up with that includes:
- A multi-project gradle build,
- Java 9 modules support,
- IntelliJ IDEA integration,
- Kotlin language modules with support for cross-references between Java and Kotlin code in the same module.
| plugins { | |
| id 'idea' | |
| id 'com.zyxist.chainsaw' version '0.3.1' apply false | |
| id "org.jetbrains.kotlin.jvm" version "1.2.31" apply false | |
| } | |
| subprojects { | |
| apply plugin: 'idea' | |
| apply plugin: 'java-library' | |
| apply plugin: 'com.zyxist.chainsaw' | |
| } | |
| // The idea plugin derives the JDK name as '1.9' while IDEA uses '9' as the default name for JDK 9 | |
| idea.project.jdkName = '9' |
| apply plugin: 'org.jetbrains.kotlin.jvm' | |
| dependencies { | |
| implementation "org.jetbrains.kotlin:kotlin-stdlib" | |
| } | |
| // Enable Kotlin compilation to Java 8 class files wiht method parameter name metadata | |
| compileKotlin.kotlinOptions.jvmTarget = '1.8' | |
| compileKotlin.kotlinOptions.javaParameters = true | |
| // As per https://stackoverflow.com/a/47669720 | |
| // See also https://discuss.kotlinlang.org/t/kotlin-support-for-java-9-module-system/2499/9 | |
| compileKotlin.destinationDir = compileJava.destinationDir | |
| jar.duplicatesStrategy = "exclude" | |
| // Allow cross-references between java and kotlin | |
| sourceSets.main.kotlin.srcDirs += 'src/main/java' |
Here is an proof-of-concept example of the above build scripts in action: https://github.com/nikolaybotevb/gradle-java9-kotlin.