Jackson XML Polymorph List

JacksonXMLPoly.kts

import com.fasterxml.jackson.databind.DeserializationFeature
import com.fasterxml.jackson.databind.MapperFeature
import com.fasterxml.jackson.databind.SerializationFeature
import com.fasterxml.jackson.dataformat.xml.JacksonXmlModule
import com.fasterxml.jackson.dataformat.xml.XmlMapper
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
import com.fasterxml.jackson.module.kotlin.KotlinModule
import com.fasterxml.jackson.module.kotlin.readValue


@JacksonXmlRootElement
class Parent {
    @JacksonXmlProperty(localName = "Book")
    @JacksonXmlElementWrapper(useWrapping = false)
    var books: List<Book> = ArrayList()
        set(value) {
            field = books + value
        }
}

data class Book(
    @JacksonXmlProperty
    val title: String
)

val kotlinModule: KotlinModule = KotlinModule.Builder()
    .strictNullChecks(false)
    .nullIsSameAsDefault(true) // needed, else it will break for null https://github.com/FasterXML/jackson-module-kotlin/issues/130#issuecomment-546625625
    .build()

val xmlMapper =
    XmlMapper(JacksonXmlModule())
        .registerModule(kotlinModule)
        .registerModule(JavaTimeModule())
        .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS) // to parse the dates as LocalDate, else parsing error
        .enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES)
        .enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT)
        .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)

val input = """
    <Parent>
        <Book title="Book 1" />
        <Something />
        <Book title="Book 2" />
        <Something />
        <Book title="Book 3" />
    </Parent> 
""".trimIndent()

val mappedValues = xmlMapper.readValue<Parent>(input)

println(mappedValues.books)
// outputs [Book(title=Book 1), Book(title=Book 2), Book(title=Book 3)]