AuthorDto.kt

class AuthorDto {

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

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

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

    @JsonProperty("birthDate")
    @JsonFormat(pattern = "MM/dd/yyyy")
    var birthDate: Date? = null

    @JsonProperty("books")
    var books: List<BookDto> = ArrayList()

}

BookDto.kt

class BookDto {

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

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

    @JsonProperty("releaseDate")
    @JsonFormat(pattern = "MM/dd/yyyy")
    var releaseDate: Date? = null

}