java - JAXB:泛型的多态性

Question

我正在尝试使用 JAXB(在 Jersey 内部)通过泛型实现多态性:

@XmlRootElement
public class Performance<M extends IMeasurement> {

    @XmlAnyElement
    private List<M> measurement;   
}

@XmlJavaTypeAdapter(MeasurementAbstract.Adapter.class)
public interface IMeasurement<D extends Serializable, V extends Number>
        extends Serializable {

    D getDate();    
    void setDate(D date);    
    V getValue();    
    void setValue(V value);
}

@XmlTransient
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({MeasurementStringDouble.class, MeasurementStringInteger.class})
public abstract class MeasurementAbstract<D extends Serializable, V extends Number> implements IMeasurement<D, V> {

    @XmlElement
    protected D date;
    @XmlElement
    protected V value;

    static class Adapter extends XmlAdapter<MeasurementAbstract, IMeasurement> {
        public IMeasurement unmarshal(MeasurementAbstract m) { return m; }
        public MeasurementAbstract marshal(IMeasurement v) { return (MeasurementAbstract) v; }
    }
}

@XmlRootElement
public class MeasurementStringDouble extends MeasurementAbstract<String, Double> {}

@XmlRootElement
public class MeasurementStringInteger extends MeasurementAbstract<String, Integer> {}

我有这个错误:

GRAVE: Mapped exception to response: 500 (Internal Server Error) javax.ws.rs.WebApplicationException: javax.xml.bind.MarshalException - with linked exception: [javax.xml.bind.JAXBException: class org.test.jaxb.MeasurementStringDouble nor any of its super class is known to this context.]

Answer 1

我找到了解决这个问题的办法:

@XmlRootElement
public class Performance<M extends IMeasurement> {

    @XmlElementWrapper(name = "measurementsPerformance")
    @XmlElements({
        @XmlElement(name = "measurement", type = MeasurementStringDouble.class),
        @XmlElement(name = "measurement", type = MeasurementStringInteger.class)})
    private List<M> measurement;   
}

public interface IMeasurement<D extends Serializable, V extends Number> extends Serializable {

    D getDate();    
    void setDate(D date);    
    V getValue();    
    void setValue(V value);
}

@XmlTransient
public abstract class MeasurementAbstract<D extends Serializable, V extends Number> implements IMeasurement<D, V>, Serializable {

    protected D date;
    protected V value;
}

@XmlRootElement
@XmlAccessorType(XmlAccessType.PROPERTY)
public class MeasurementStringDouble extends MeasurementAbstract<String, Double> {

    @XmlElement
    @Override
    public String getDate() {
        return date;
    }

    @XmlElement
    @Override
    public Double getValue() {
        return value;
    }
}

@XmlRootElement
@XmlAccessorType(XmlAccessType.PROPERTY)
public class MeasurementStringInteger extends MeasurementAbstract<String, Integer> {

    @XmlElement
    @Override
    public String getDate() {
        return date;
    }

    @XmlElement
    @Override
    public Integer getValue() {
        return value;
    }
}

此解决方案的缺点是在子类中重复了 getter/setter。