JAXB: how to unmarshal a List of objects of different types but with common parent?

Question

There is a fairly common pattern in our applications. We configure a configure a set (or list) of objects in Xml, which all implement a common interface. On start-up, the

Answer 1

You could use an XmlAdapter for this use case. The impl bleow handles just the Commission type but could be easily extended to support all the types. You need to ensure that AdaptedFee contains the combined properties from all the implementations of the Fee interface.

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class FeeAdapter extends XmlAdapter{

    public static class AdaptedFee {

        @XmlAttribute
        public String type;

        @XmlAttribute
        public String name;

        @XmlAttribute
        public String rate;

    }

    @Override
    public AdaptedFee marshal(Fee fee) throws Exception {
        AdaptedFee adaptedFee = new AdaptedFee();
        if(fee instanceof Commission) {
            Commission commission = (Commission) fee;
            adaptedFee.type = "Commission";
            adaptedFee.name = commission.name;
            adaptedFee.rate = commission.rate;
        }
        return adaptedFee;
    }

    @Override
    public Fee unmarshal(AdaptedFee adaptedFee) throws Exception {
        if("Commission".equals(adaptedFee.type)) {
            Commission commission = new Commission();
            commission.name = adaptedFee.name;
            commission.rate = adaptedFee.rate;
            return commission;
        }
        return null;
    }

}

An XmlAdapter is configured using the @XmlJavaTypeAdapter annotation:

import java.util.List;
import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Fees {

    @XmlElement(name="fee")
    @XmlJavaTypeAdapter(FeeAdapter.class)
    private List fees;

}

For More Information

• http://blog.bdoughan.com/2012/01/jaxb-and-inhertiance-using-xmladapter.html