JAXB 无法解组

Question

I cannot unmarshall a generic Type, like this. I do not like it solve with an adapter class. Can someone help..

interface Car {
}


class Car1 implements Car {
}

class Car2 implements Car {
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType( name = "", propOrder = { "car1" } )
@XmlRootElement(name = "Element")
class Element{

@XMLELEMENT(type="Car1.class" name="Car")
private Car car1;

}

Answer 1

If the xml you try to unmarshall has different tag for describing car1 and car2, then it is possible by using @XmlElements annotation.

I am creating a small example below to show case it:

@XmlRootElement
public class SomeRoot {

    @XmlElements({
            @XmlElement(type = Car1.class, name = "car1"),
            @XmlElement(type = Car2.class, name = "car2")
    })
    private List<Car> cars;
}

Then your interface:

public interface Car {
}

A base class with some common field:

@XmlAccessorType(XmlAccessType.FIELD)
public class BaseCar {

    private String type;
}

And implementation for car1:

@XmlAccessorType(XmlAccessType.FIELD)
public class Car1 extends BaseCar implements Car {
    private String car1SpecificField;

}

and car2:

@XmlAccessorType(XmlAccessType.FIELD)
public class Car2 extends BaseCar implements Car {
    private String car2SpecificField;
}

This would unmarshal the xml below fine:

<someRoot>
    <car1>
        <type>some type</type>
        <car1SpecificField>some value</car1SpecificField>
    </car1>
    <car2>
        <type>other type</type>
        <car2SpecificField>other value</car2SpecificField>
    </car2>
</someRoot>

If your xml has the <car> instead of <car1> and <car2> you need to use an adapter or else jaxb doesn't know to which class to unmarshall.