Tonel

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
	id("org.springframework.boot") version "2.3.1.RELEASE"
	id("io.spring.dependency-management") version "1.0.9.RELEASE"
	kotlin("jvm") version "1.3.72"
	kotlin("plugin.spring") version "1.3.72"
	kotlin("kapt") version "1.3.72"
}

Tonel

class Author {
    var id: Int? = null

    var name: String? = null

    var surname: String? = null

    var birthDate: Date? = null

    val books: MutableList<Book> = ArrayList()

Tonel

class AuthorDto {
    @JsonProperty("id")
    var id: Int? = null

    @JsonProperty("name")
    var name: String? = null

    @JsonProperty("surname")
    var surname: String? = null

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class SpecialAuthorDto {
    var name: String? = null

    var surname: String? = null

    // no birthDate

    var firstBook : BookDto? = null
}

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@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
interface AuthorMapper {

    fun authorToAuthorDto(
        author : Author
    ) : AuthorDto

    fun authorsToAuthorDtos(
        authors : List<Author>
    ) : List<AuthorDto>

Tonel

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2020-06-28T09:24:47+0200",
    comments = "version: 1.3.1.Final, compiler: javac, environment: Java 13.0.2 (Oracle Corporation)"
)
@Component
public class AuthorMapperImpl implements AuthorMapper {

    @Override
    public AuthorDto authorToAuthorDto(Author author) {

Tonel

@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
abstract class SpecialAuthorMapper {

    // author's book property is accessed through java setter
    @Mappings(
        Mapping(target="firstBook", expression = "java(booksToFirstBook(author.getBooks()))")
    )
    abstract fun authorToSpecialAuthorDto(
        author : Author
    ) : SpecialAuthorDto

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@RestController
@RequestMapping("/authors")
class AuthorController {
    @Autowired
    lateinit var authorRepository: AuthorRepository

    @Autowired
    lateinit var authorMapper: AuthorMapper

    @Autowired

Tonel

@Entity
@Table(name = "post")
public class Post {

    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;

    @Column(name = "title")

Tonel

@Entity
@Table(name = "post")
data class Post(
    @get:Id
    @get:GeneratedValue
    @get:Column(name = "id")
    val id: Long,

    @get:Column(name = "title")
    val title: String,