How to unmarshall XML to this class?

Question

I would like to unmarshall XML using JAXB unmarshaller to the object of this type.

public class Pair<T1,T2> implements Serializable {
    private T1 first;

    private T2 second;

    public Pair(T1 first, T2 second) {
        this.first = first;
        this.second = second;
    }

    public T1 getFirst() {
        return first;
    }

    public void setFirst(T1 first) {
        this.first = first;
    }

    public T2 getSecond() {
        return second;
    }

    public void setSecond(T2 second) {
        this.second = second;
    }
}


public class TripPair<T1,T2> extends Pair<T1,T2> {

    public TripPair(T1 first, T2 second) {
        super(first, second);
    }
}

public class Fare extends Pricing implements Comparable<Fare> {

    private List<TripPair<Integer,Integer>> trips = new LinkedList<>();
}

XML file

<fareGroups>
    <trips>
        <second>37</second>
        <first>0</first>
    </trips>
</fareGroups>

XML file have also other data and it is unmarshalled, unfortunately data from elements first and second are not unmarshalled. I tried to add @XmlElement annotations on these fields to Pair class, but without sucesss.

Using XmlAdapter

public class PairAdapter extends XmlAdapter<String, Integer> {

    public String marshal(Integer val) throws Exception {
        return val.toString();
    }

    public Integer unmarshal(String val) throws Exception {
        return Integer.valueOf(val);
    }
}

public class Pair<T1,T2> implements Serializable {
    @XmlJavaTypeAdapter(PairAdapter.class)
    private T1 first;

    @XmlJavaTypeAdapter(PairAdapter.class)
    private T2 second;
}

Answer 1

You will need to add a zero-arg constructor, or create an XmlAdapter for the Pair class to get it to unmarshal correctly (see: http://blog.bdoughan.com/2010/12/jaxb-and-immutable-objects.html ).

UPDATE

I'm using JAXB marshaller for it and when I made a debugging of non-marshalled element, it has wrong type. ElementNSImpl instead of Integer.

As far as JAXB is concerned first and second will be treated as type Object , since it derives metadata at the class level Pair instenad of the type level Pair<Integer, Integer> . Because of this the XML will need to qualify the XML elements with the necessary type information. This is done using the xsi:type attribute.

public class Pair<T1,T2> implements Serializable {
    private T1 first;

    private T2 second;

Try populating your object model with the data you want and then marshalling it and you will see what the XML should look like for the unmarshal operation.