MOXy JAXB - Map Interfaces to XML

I recently came across a Twitter message (tweet) complaining that JAXB does not support binding Java interfaces to XML. Below I'll describe how this can be accomplished using MOXy in the upcoming EclipseLink 2.1.1 and 2.2 releases (try it now).


Below is the model we'll be using, notice how everything is an interface:

package example.interfaces;

import java.util.List;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement()
@XmlType(propOrder={"name", "address"})
public interface Customer {

    String getName();
    void setName(String name);

    Address getAddress();
    void setAddress(Address address);

    public List<PhoneNumber> getPhoneNumbers();
    public void setPhoneNumbers(List<PhoneNumber> phoneNumbers);

}

package example.interfaces;

public interface Address {

    public String getStreet();
    public void setStreet(String street);
 
    public String getCity();
    public void setCity(String city);

}

package example.interfaces;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlValue;

public interface PhoneNumber {

    @XmlAttribute()
    String getType();
    void setType(String type);

    @XmlValue()
    String getValue();
    void setValue(String value);

}

We need a way to create an instance of the interface.  For this we'll leverage an ObjectFactory.  There is some flexibility on how this could be done, but I'll use Java's proxy mechanism with an InvocationHandler.

package example.interfaces;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;
import javax.xml.bind.annotation.XmlRegistry;
 
@XmlRegistry
public class ObjectFactory {
 
    public Customer createCustomer() {
        return createInstance(Customer.class);
    }
 
    public Address createAddress() {
        return createInstance(Address.class);
    }
 
    public PhoneNumber createPhoneNumber() {
        return createInstance(PhoneNumber.class);
    }
 
    private <T> T createInstance(Class<T> anInterface) {
        return (T) Proxy.newProxyInstance(anInterface.getClassLoader(), new Class[] {anInterface}, new InterfaceInvocationHandler());
    }
 
    private static class InterfaceInvocationHandler implements InvocationHandler {
 
        private Map<String, Object> values = new HashMap<String, Object>();
 
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            String methodName = method.getName();
            if(methodName.startsWith("get")) {
                return values.get(methodName.substring(3));
            } else {
                values.put(methodName.substring(3), args[0]);
                return null;
            }
        }
 
    }

}

Now we can run the following code to see everything working:

package example.interfaces;

import java.io.FileInputStream;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jaxbContext = JAXBContext.newInstance(ObjectFactory.class);

        FileInputStream xml = new FileInputStream("input.xml");
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        Customer customer = (Customer) unmarshaller.unmarshal(xml);

        ObjectFactory objectFactory = new ObjectFactory();
        PhoneNumber homePhoneNumber = objectFactory.createPhoneNumber();
        homePhoneNumber.setType("home");
        homePhoneNumber.setValue("613-555-3333");
        customer.getPhoneNumbers().add(homePhoneNumber);

        Marshaller marshaller = jaxbContext.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }

}

To use the MOXy runtime, you need to add a file named jaxb.properties in with your model classes (or interfaces) with the following entry:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

Now back to Twitter to mine more topics for future blog posts.