MOXy JSON支持

@XmlRootElement
@XmlDiscriminatorNode("@type")
public abstract class Entity {

    public Entity(){}

    public Entity(String id){
        this.id = id;
    }

    private String id;

    @XmlElement
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
}

@XmlRootElement
@XmlDiscriminatorValue("photo")
public class Photo extends Entity{

    private String thumbnail;

    public Photo(){}

    public Photo(String id) {
        super(id);
    }

    public void setThumbnail(String thumbnail) {
        this.thumbnail = thumbnail;
    }

    @XmlElement(name="thumbnail")
    public String getThumbnail() {
        return thumbnail;
    }
}

<object type="photo">
   <id>photoId423423</id>
   <thumbnail>http://dsadasadas.dsadas</thumbnail>
</object>

"object":{"id":"photoId423423"}