Question

Edit: I originally left out what may be an important detail from my question — My service methods that return Java objects to be marshaled return an interface type (Foo) rather than the class implementation type (FooImpl).

I have a simple Java class with JAX-B annotations for several elements and attributes:

@XmlRootElement(name = "foo")
public class FooImpl {
    private String id;
    private String name;

    @XmlElement
    public String getName() {
            return name;
    }

    public void setName(final String name) {
            this.name = name;
    }

    @XmlAttribute
    public String getId() {
            return Id;
    }

    public void setId(final String id) {
            this.id = id;
    }
}

Edit: The FooImpl class has an interface named Foo:

public interface Foo {
    public String getName();
    public void setName(final String name);

    public String getId();
    public void setId(final String id);
}

When I have a service method that returns a Foo, I get what I expect:

<foo id="abc123">
  <name>bar</name>
</foo>

But I also have another class that contains a List<Foo> and when it is marshalled, the XML elements for foo do not contain their id attribute!!

<foos>
    <foo>
      <name>bar1</name>
    </foo>
    <foo>
      <name>bar2</name>
    </foo>
</foos>

The class that holds the list looks like this:

@XmlRootElement(name = "foos")
public class Foos {

    private List<Foo> foos;

    @XmlElement(name = "foo")
    public List<Foo> getFoos() {
        return foos;
    }

    public void setFoos(List<Foo> foos) {
        this.foos = foos;
    }

}

I happen to be using MOXy as my JAX-B implementation, but I do not think that matters.

Answer 1

Note: I’m the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

Since you have a property whose type is an interface you will need to specify the implementing type on the @XmlElement annotation:

@XmlElement(name = "foo", type=FooImpl.class)
public List<Foo> getFoos() {
   return foos;
}

Below is a complete example:

Foos

package forum9137171;

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

@XmlRootElement(name = "foos")
public class Foos {

    private List<Foo> foos;

    @XmlElement(name = "foo", type=FooImpl.class)
    public List<Foo> getFoos() {
        return foos;
    }

    public void setFoos(List<Foo> foos) {
        this.foos = foos;
    }

}

Foo

package forum9137171;

public interface Foo {
    public String getName();
    public void setName(final String name);

    public String getId();
    public void setId(final String id);
}

FoomImpl

package forum9137171;

import javax.xml.bind.annotation.*;

@XmlRootElement(name = "foo")
public class FooImpl implements Foo {
    private String id;
    private String name;

    @XmlElement
    public String getName() {
            return name;
    }

    public void setName(final String name) {
            this.name = name;
    }

    @XmlAttribute
    public String getId() {
            return id;
    }

    public void setId(final String id) {
            this.id = id;
    }
}

Demo

package forum9137171;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Foos.class);
        System.out.println(jc);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum9137171/input.xml");
        Foos foos = (Foos) unmarshaller.unmarshal(xml);

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

}

Input/Output

org.eclipse.persistence.jaxb.JAXBContext@16a786
<?xml version="1.0" encoding="UTF-8"?>
<foos>
   <foo id="abc123">
      <name>bar1</name>
   </foo>
   <foo id="def456">
      <name>bar2</name>
   </foo>
</foos>

For More Information

• http://blog.bdoughan.com/2011/05/jaxb-and-interface-fronted-models.html