Unmarshall JAXB marshalled List failing with NullPointerExceptin

Question

I have a list of Person objects within a ListWrapper and every Person object contains a list of telefonnummbers. Marschalling via JAXB.marschall(file, PersonList.class) is working fine. The problem is the unmarshalling. I get an NullPointerException, see stacktrace below. I suspect missing or wrong annotations but i can't figure it out by myself...

Code

public class TelefonNr {[..]}
public class Person {
  [..]
  List<TelefonNr> telefonNrs;
  [..]
  @XmlElement(name = "number")
  @XmlElementWrapper(name = "telefonnumbers")
  public List<TelefonNr> getTelefonNrs(){
    return this.telefonNrs;
  }
  [..]
}
@XmlRootElement(name = "persons")
public class PersonList {
  List<Person> persons;
  [..]
  @XmlElement(name = "person")
public List<Person> getPersons() {
    return this.Persons;
}
  [..]
}

Exceptions stacktrace

at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Lister.java:289)
at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Lister.java:253)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Scope.add(Scope.java:106)
at com.sun.xml.internal.bind.v2.runtime.property.ArrayERProperty$ReceiverImpl.receive(ArrayERProperty.java:198)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.endElement(UnmarshallingContext.java:523)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.SAXConnector.endElement(SAXConnector.java:143)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:609)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2973)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:117)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:648)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:203)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:175)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:157)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:162)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:171)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:189)
at org.twinhowi.organizer.core.DatastructureDemo.testUnmarshalling(DatastructureDemo.java:131)
at org.twinhowi.organizer.core.DatastructureDemo.main(DatastructureDemo.java:144)

Answer 1

Theory:

You may have to initialize the collection - either eager or lazy.

List<TelefonNr> telefonNrs = new LinkedList<TelefonNr>();

Or:

public List<Person> getPersons() {
    if (this.persons == null) {
       this.persons =  new LinkedList<Person>();
    }
    return this.persons;
}

But see also this question:

Help troubleshooting JAXB unmarshalling NPE