JAXB and Inheritance - Using XmlAdapter

In previous posts I have covered how to map inheritance relationships in JAXB. This can be done by element name (via @XmlElementRef), by the xsi:type attribute, or in EclipseLink MOXy using another XML attribute (via @XmlDescriminatorNode/@XmlDescriminatorValue).  In this post the type indicator will be an XML attribute/element unique to that type, and we will leverage an XmlAdapter to implement this behaviour.

Input (input.xml)

<?xml version="1.0" encoding="UTF-8"?>
<customer>
    <contact-method
        number="555-1111"/>
    <contact-method
        street="1 A St"
        city = "Any Town"/>
    <contact-method
        number="555-2222"/>
</customer>

package blog.inheritance.xmladapter;
 
import java.util.List;
import javax.xml.bind.annotation.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    @XmlElement(name="contact-method")
    private List<ContactMethod> contactMethods;
 
}

package blog.inheritance.xmladapter;
 
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
@XmlJavaTypeAdapter(ContactMethodAdapter.class)
public abstract class ContactMethod {
 
}

package blog.inheritance.xmladapter;
 
public class Address extends ContactMethod {
 
    protected String street;
    protected String city;
 
}

package blog.inheritance.xmladapter;
 
public class PhoneNumber extends ContactMethod {
 
    protected String number;
 
}

package blog.inheritance.xmladapter;
 
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.adapters.XmlAdapter;
 
public class ContactMethodAdapter extends
    XmlAdapter<ContactMethodAdapter.AdaptedContactMethod, ContactMethod> {
 
    @Override
    public AdaptedContactMethod marshal(ContactMethod contactMethod)
        throws Exception {
        if (null == contactMethod) {
            return null;
        }
        AdaptedContactMethod adaptedContactMethod = new AdaptedContactMethod();
        if (contactMethod instanceof Address) {
            Address address = (Address) contactMethod;
            adaptedContactMethod.street = address.street;
            adaptedContactMethod.city = address.city;
        } else {
            PhoneNumber phoneNumber = (PhoneNumber) contactMethod;
            adaptedContactMethod.number = phoneNumber.number;
        }
        return adaptedContactMethod;
    }
 
    @Override
    public ContactMethod unmarshal(AdaptedContactMethod adaptedContactMethod)
        throws Exception {
        if (null == adaptedContactMethod) {
            return null;
        }
        if (null != adaptedContactMethod.number) {
            PhoneNumber phoneNumber = new PhoneNumber();
            phoneNumber.number = adaptedContactMethod.number;
            return phoneNumber;
        } else {
            Address address = new Address();
            address.street = adaptedContactMethod.street;
            address.city = adaptedContactMethod.city;
            return address;
        }
    }
 
    public static class AdaptedContactMethod {
 
        @XmlAttribute
        public String number;
 
        @XmlAttribute
        public String street;
 
        @XmlAttribute
        public String city;
 
    }
 
}

package blog.inheritance.xmladapter;
 
import java.io.File;
import javax.xml.bind.*;
 
public class Demo {
 
    public static void main(String[] args) throws Exception  {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);
 
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/blog/inheritance/xmladapter/input.xml");
        Customer customer = (Customer) unmarshaller.unmarshal(xml);
 
        for(ContactMethod contactMethod : customer.getContactMethods()) {
            System.out.println(contactMethod.getClass());
        }
 
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }
 
}

class blog.inheritance.xmladapter.PhoneNumber
class blog.inheritance.xmladapter.Address
class blog.inheritance.xmladapter.PhoneNumber
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <contact-method number="555-1111"/>
    <contact-method city="Any Town" street="1 A St"/>
    <contact-method number="555-2222"/>
</customer>

• eclipselink/Moxy : inheritance and attribute name overloading based on type
• Jaxb objects with the same name
• Java/JAXB: Unmarshal XML attributes to specific Java object attributes

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