MapStruct with Kotlin

Example usage of MapStruct and Kotlin with JDK-8 Bytecode. This is achieved by using the Kotlin Annotation Processing Tool (KAPT).

Code

In this example we want to map between a Person (Model) and a PersonDto (DTO).

data class Person(var firstName: String?, var lastName: String?, var phoneNumber: String?, var birthdate: LocalDate?) {
    // Necessary for MapStruct
    constructor() : this(null, null, null, null)
}

data class PersonDto(var firstName: String?, var lastName: String?, var phone: String?, var birthdate: LocalDate?) {
    // Necessary for MapStruct
    constructor() : this(null, null, null, null)
}

The MapStruct converter:

@Mapper
interface PersonConverter {

    @Mapping(source = "phoneNumber", target = "phone")
    fun convertToDto(person: Person) : PersonDto

    @InheritInverseConfiguration
    fun convertToModel(personDto: PersonDto) : Person

}

Usage:

val converter = Mappers.getMapper(PersonConverter::class.java) // or PersonConverterImpl()

val person = Person("Samuel", "Jackson", "0123 334466", LocalDate.of(1948, 12, 21))

val personDto = converter.convertToDto(person)
println(personDto)

val personModel = converter.convertToModel(personDto)
println(personModel)

Multiple Mappings

As of Kotlin 1.1, repeated annotations are not supported (see KT-12794). You have to wrap the Mapping-Annotation in a Mappings-Annotation.

    @Mappings(
            Mapping(source = "majorVersion", target = "major"),
            Mapping(source = "minorVersion", target = "minor"),
            Mapping(source = "patchVersion", target = "patch"),
            Mapping(source = "normalVersion", target = "normal"),
            Mapping(source = "preReleaseVersion", target = "preRelease")
    )
    fun convertToDto(version: Version): VersionDto

Further documentation

Using kapt: https://kotlinlang.org/docs/reference/kapt.html

MapStruct: http://mapstruct.org/

Kotlin: https://kotlinlang.org/

Maven Setup

Add mapstruct to your dependencies

<dependency>
  <groupId>org.mapstruct</groupId>
  <artifactId>mapstruct</artifactId>
  <version>${mapstruct.version}</version>
</dependency>

Add an execution to the kotlin-maven-plugin with the kapt goal and mapstruct as annotation processor:

<plugin>
  <groupId>org.jetbrains.kotlin</groupId>
  <artifactId>kotlin-maven-plugin</artifactId>
  <version>${kotlin.version}</version>
  <executions>
    <execution>
        <id>kapt</id>
        <goals>
            <goal>kapt</goal>
        </goals>
        <configuration>
            <sourceDirs>
                <sourceDir>src/main/kotlin</sourceDir>
                <sourceDir>src/main/java</sourceDir>
            </sourceDirs>
            <annotationProcessorPaths>
                <annotationProcessorPath>
                    <groupId>org.mapstruct</groupId>
                    <artifactId>mapstruct-processor</artifactId>
                    <version>${mapstruct.version}</version>
                </annotationProcessorPath>
            </annotationProcessorPaths>
        </configuration>
    </execution>
  ...
  </executions>
  ....
</plugin>