Question

Reflecting on JAXB annotated objects, is there a way to determine if a class/field/method will result in a xsi:type attributed during marshaling?

Is XmlElement annotation,
annotation.type != javax.xml.bind.annotation.XmlElement.DEFAULT.class
the only case I need to worry about?

I’m writing a Lua unmarshaler where we have dropped much of the usual xml type info and I’m trying to figure-out how to match the incoming Lua to JAXB.

Thanks.

–Update–

Here is simple example that shows the problem:

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
@XmlSeeAlso({ Cat.class, Dog.class })
public class Animal {
  @XmlElement()
  public List<Animal> critters;
  @XmlAttribute
  public String type;
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
public class Dog extends Animal {
  public Dog() {
    this.type = "German Shepherd";
  }
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement()
public class Cat extends Animal {
  public Cat() {
    this.type = "Black";
  }
}

When I receive an Animal object can I query critter’s annotation to detect that it should be a Dog or Cat and not an Animal?

Answer 1

There are a couple circumstances where a JAXB (JSR-222) implementation will write out an xsi:type attribute.

1. If the field/property is of type Object (or is annotated with @XmlElement(type=Object.class)) and not mapped with @XmlAnyElement(lax=true) and holds an instance of an Object that the JAXBContext has mappings for.
2. The default mechanism for representing inheritance will result in an xsi:type attribute to represent subclasses (see: http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-xsitype.html).