jaxb-01.scala

import javax.xml.bind.annotation._

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
case class Person(fullname: String, username: Option[String], age: Int)

jaxb-02.scala

import scala.annotation.target.field

import javax.xml.bind.annotation._
import javax.xml.bind.annotation.adapters._
import java.util.{List => JList}
import java.util.{ArrayList => JArrayList}
import java.util.{Arrays => JArrays}
import common.Types.{xmlElements, xmlTypeAdapter, xmlElement}

type xmlElement     = XmlElement @field
type xmlTypeAdapter = XmlJavaTypeAdapter @field
type xmlElements = XmlElements @field

class StringOptionAdapter extends OptionAdapter[String](null, "")
class OptionAdapter[A](nones: A*) extends XmlAdapter[A, Option[A]] {
  def marshal(v: Option[A]): A = v.getOrElse(nones(0))
  def unmarshal(v: A) = if (nones contains v) None else Some(v)
}

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
case class Person(
   @xmlElement(required = true) fullname: String,
   @xmlTypeAdapter(classOf[StringOptionAdapter]) username: Option[String],
   age: Int,
   @XmlElementWrapper favNumbers: FavNumbers){

  // only needed and accessed by JAXB
  private def this() = this("", None, 0, FavNumbers(new JArrayList[Int]))
}

@XmlAccessorType(XmlAccessType.FIELD)
case class FavNumbers(
   @xmlElements(
     value = Array(new xmlElement(name="favNumber", `type` = classOf[Int]))
   )
   favNumbers: JList[Int]
){
  private def this() = this(new JArrayList[Int])
}

jaxb-03.scala

import javax.xml.bind._
import javax.xml.transform.stream.StreamResult

val context = JAXBContext.newInstance(classOf[Person])

context.generateSchema(new SchemaOutputResolver {
  def createOutput(namespaceUri: String, suggestedFileName: String) = {
    val res = new StreamResult(System.out)
    res.setSystemId(suggestedFileName)
    res
  }
})

jaxb-04.xsd

<xs:schema version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xs:element name="person" type="person"/>
	<xs:complexType name="person">
		<xs:sequence>
			<xs:element name="fullname" type="xs:string"/>
			<xs:element name="username" type="xs:string" minOccurs="0"/>
			<xs:element name="age" type="xs:int"/>
			<xs:element name="favNumbers">
				<xs:complexType>
					<xs:sequence>
						<xs:element name="favNumber" type="xs:integer" minOccurs="0" maxOccurs="unbounded"/>
					</xs:sequence>
				</xs:complexType>			
			</xs:element>
		</xs:sequence>
	</xs:complexType>
</xs:schema>

jaxb-05.scala

context.createMarshaller.marshal(Person("Martin Krasser", Some("krasserm"), 30 /* haha */), System.out)

jaxb-06.xml

<person>
  <fullname>Martin Krasser</fullname>
  <username>krasserm</username>
  <age>30</age>
</person>

jaxb-07.scala

    val personXml1 = "<person><fullname>Martin Krasser</fullname><username>mrt1nz</username><age>30</age><favNumbers><favNumber>73</favNumber><favNumber>47</favNumber></favNumbers></person>"
    val personXml2 = "<person><fullname>Martin Krasser</fullname><age>30</age><favNumbers /></person>"

    assert(context.createUnmarshaller().unmarshal(new StringReader(personXml1)) ==
      Person("Martin Krasser", Some("mrt1nz"), 30, FavNumbers(new JArrayList[Int](JArrays.asList(73,47)))))

    assert(context.createUnmarshaller().unmarshal(new StringReader(personXml2)) ==
      Person("Martin Krasser", None, 30, FavNumbers(new JArrayList[Int])))