JAXB Object won't marshal/unmarshal List property - list

Question

With the following:
#XmlRootElement(name = "purchase")
#XmlType(propOrder = {"memberId", "propertyA", "propertyB", "propertyC", "listProps"})
public class ClassA {
private Long memberId;
private Integer propertyA;
private String propertyB;
private Integer propertyC;
private List<ClassB> listProps;
public ClassA() {
}
#XmlElement(name = "memberId")
public Long getMemberId() {
return memberId;
}
public void setMemberId(Long memberId) {
this.memberId = memberId;
}
#XmlElement(name = "propertyA")
public Integer getPropertyA() {
return propertyA;
}
public void setPropertyA(Integer propertyA) {
this.propertyA = propertyA;
}
#XmlElement(name = "propertyB")
public String getPropertyB() {
return propertyB;
}
public void setPropertyB(String propertyB) {
this.propertyB = propertyB;
}
#XmlElement(name = "propertyC")
public Integer getPropertyC() {
return propertyC;
}
public void setPropertyC(Integer propertyC) {
this.propertyC = propertyC;
}
#XmlElement(name = "listProps")
public List<ClassB> getListProps() {
return listProps;
}
public void setListProps(List<ClassB> listProps) {
this.listProps = listProps;
}
}
#XmlRootElement(name = "listProp")
#XmlType(propOrder = {"countA", "countB"})
public class ClassB {
private int countA;
private int countB;
public ClassB() {
}
public int getCountA() {
return countA;
}
public int getCountB() {
return countB;
}
#XmlElement(name = "countA")
public void setCountA(int countA) {
this.countA = countA;
}
#XmlElement(name = "countB")
public void setCountB(int countB) {
this.countB = countB;
}
}
When I try and marshal / unmarshal objects of type ClassA, the listProps is always empty regardless of how many objects I have put in it. Can anyone tell me what I am doing wrong?

Answer 1

When I marshal your model classes as follows:
import java.util.*;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(ClassA.class);
List<ClassB> classBs = new ArrayList<ClassB>();
classBs.add(new ClassB());
classBs.add(new ClassB());
ClassA classA = new ClassA();
classA.setListProps(classBs);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(classA, System.out);
}
}
I get the following output, so there is no problem with your list property:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<purchase>
<listProps>
<countA>0</countA>
<countB>0</countB>
</listProps>
<listProps>
<countA>0</countA>
<countB>0</countB>
</listProps>
</purchase>

Answer 2

As I understand your problem is to unmarshal list of values which you have marshaled. The same problem I faced with jaxb-impl lib +2.2.x when unmarshaling results into empty list while XML contains at least 1 element. Try to instantiate list if it is null in method getListProps so JAXB could populate it. I feel like the problem is in List + XmlAccessorType.PROPERTY as it does not create list by default and tries to use existing one, because it is null setListProps is called with empty collection.