@JacksonXmlElementWrapper doesn’t work with data classes

I want to mapping a xml using kotlin data class, my xml wrapper a list of elements in a wapper node. Xml example: <MyPojo><elements><element value="e1"/></elements></MyPojo>

Here the <element> node is a collection, wrapped in the <elements> node.

When I use the data class to map the ‘MyPojo’ and ‘element’ object and I annotated the collection property with @JacksonXmlElementWrapper and @JacksonXmlProperty it doesn’t work when I try to deserialise form xml. The exception is: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Invalid definition for property elements (of type MyDataPojo): Could not find creator property with name ‘elements’ (known Creator properties: [element])

I use :

• Java 1.8
• Kotlin 1.2.31
• Jackson: 2.9.5

I have write a test to compare the mapping using the standard class and the data class. The standard class test passed, the data class test failed.

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.module.kotlin.KotlinModule
import junit.framework.Assert.assertEquals
import org.junit.Test

/**
 * Mapping the Xml with standard classes
 */
@JacksonXmlRootElement(localName = "MyPojo")
class MyPojo {

  @JacksonXmlElementWrapper(localName = "elements")
  @JacksonXmlProperty(localName = "element")
  var list: List<MyElement>? = null

}

/**
 * Mapping the Xml with standard classes
 */
class MyElement {
  @JacksonXmlProperty(localName = "value", isAttribute = true)
  var value: String? = null

}

/**
 * Mapping the Xml with data classes
 */
@JacksonXmlRootElement(localName = "MyPojo")
data class MyDataPojo (
    @JacksonXmlElementWrapper(localName = "elements")
    @JacksonXmlProperty(localName = "element")
    val list
    : List<MyDataElement>
)

/**
 * Mapping the Xml with data classes
 */
data class MyDataElement (
    @JacksonXmlProperty(localName = "value", isAttribute = true)
    var value: String
)

class TextKotlinXmlWrapper {
  // xml example I want to deserialize
  val xml = """<MyPojo><elements><element value="e1"/></elements></MyPojo>"""

  val mapper = XmlMapper()
      .registerModule(KotlinModule())

  @Test
  @Throws(Exception::class)
  fun test_class() {

    // I create a pojo from the xml using the standard classes
    val pojoFromXml = mapper.readValue(xml, MyPojo::class.java)

    //I create a xml from the pojo
    val xmlFromPojo = mapper.writeValueAsString(pojoFromXml)

    // I compare the original xml with the xml generated from the pojo
    assertEquals(xml, xmlFromPojo)

  }

  @Test
  @Throws(Exception::class)
  fun test_data_class() {

    // I create a pojo from the xml using the data classes
    val pojoFromXml = mapper.readValue(xml, MyDataPojo::class.java)

    //I create a xml from the pojo
    val xmlFromPojo = mapper.writeValueAsString(pojoFromXml)

    // I compare the original xml with the xml generated from the pojo
    assertEquals(xml, xmlFromPojo)

  }

}

[jespeche]

Hi guys, Just in case it helps somebody else, I found a workaround by combining the things mentioned here with a property backed up with a constructor field.

This allow us to still use a data class and avoid writing getters/setters/hashcode/equals.

data class Example(private var _elements: MutableList<String>) {
    @get:JacksonXmlElementWrapper(localName = "elements")
    @get:JacksonXmlProperty(localName = "element")
    var elements
        set(value) { _elements = value }
        get() = _elements
}

It is not too elegant, but it works fine so hopefully it will help.

Thanks guys for helping me figuring it out!

[joffrey-bion]

FYI, from Kotlin you can specify where the annotation lands, using the get: or field: prefixes between the @ and the annotation name. So the following should work:

data class Example(
        @get:JacksonXmlElementWrapper(localName = "elements")
        @get:JacksonXmlProperty(localName = "element")
        val elements: MutableList<String>
)