JAXB: how to unmarshal a List of objects of different types but with common parent?

Question

There is a fairly common pattern in our applications. We configure a configure a set (or list) of objects in Xml, which all implement a common interface. On start-up, the

Answer 1

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

If you are using MOXy as your JAXB provider then you could use the MOXy's @XmlPaths annotation to extend the standard JAXB @XmlElements annotation to do the following:

Fees

import java.util.List;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.*;

@XmlRootElement
public class Fees {

    @XmlElements({
        @XmlElement(type=Commission.class),
        @XmlElement(type=FINRAPerShare.class),
        @XmlElement(type=SEC.class),
        @XmlElement(type=Route.class)
    })
    @XmlPaths({
        @XmlPath("fee[@type='Commission']"),
        @XmlPath("fee[@type='FINRAPerShare']"),
        @XmlPath("fee[@type='SEC']"),
        @XmlPath("fee[@type='Route']")
    })
    private List fees;

}

Commission

The implementations of the Fee interface would be annotated normally.

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Commission implements Fee {

    @XmlAttribute
    private String name;

    @XmlAttribute
    private String rate;

}

For More Information

• http://blog.bdoughan.com/2011/03/map-to-element-based-on-attribute-value.html
• http://blog.bdoughan.com/2010/10/jaxb-and-xsd-choice-xmlelements.html
• http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html