java - 解码 JAXB 编码列表因空指针异常而失败

Question

我在 ListWrapper 中有一个 Person 对象列表，每个 Person 对象都包含一个电话号码列表。通过 JAXB.marschall(file, PersonList.class) 编码工作正常。问题是解码。我得到一个 NullPointerException，请参阅下面的堆栈跟踪。我怀疑注释丢失或错误，但我自己无法弄清楚...

代码

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;
}
  [..]
}

异常堆栈跟踪

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

理论:

您可能必须初始化集合 - 急切或懒惰。

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

或者:

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

但另见这个问题:

Help troubleshooting JAXB unmarshalling NPE