JAXB-Eclipselink: Mapping abstract “getter” to XML

问题

I am using the EclipseLink implementation (2.3) of JAXB to map POJOs to XML and encountering a problem with following usecase:

public abstract class A {

    public abstract Set<X> getX();
    // There is no setter
}


public class B extends A {

    // Set via constructor
    private Set<X> x;

    @Override
    public Set<X> getX();

}

I am defining the mapping itself completely in an external bindings-file, i set class A to be transient like so:

<java-type name="foo.A" xml-transient="true"/>

and for class B:

<java-type name="bar.B" xml-accessor-type="PROPERTY">
    <xml-root-element name="B" />
    <java-attributes>
        <xml-element java-attribute="x" xml-path="..."/>
    </java-attributes>
</java-type>

Now, upon marshalling i am getting the exception: "Duplicate Property named [x] found on class [bar.B]" which in my opinion is coming from the abstract declaration in A, being inherited by B.

Setting the accessor-type for B to FIELD, gets rid of this error, unfortunately this is not an option because i do have an extra property in B to marshal which does not return a field but a calculated value, so i am stuck with PROPERTY (following works: setting accessor-type for B to FIELD and mapping the extra property with an @XmlPath annotation - but i dont want annotations in my code).

Being stuck with accessor-type PROPERTY for class B, my next attempt was:

<java-type name="foo.A" xml-accessor-type="NONE"/>

to prevent the abstract property from being inherited by B, which gets me:

Ignoring attribute [x] on class [bar.B] as no Property was generated for it.

Same is happening using this mapping:

<java-type name="foo.A" xml-accessor-type="PROPERTY">
    <java-attributes>
        <xml-transient java-attribute="x"/>
    </java-attributes>
</java-type>

In both cases property 'x' is ignored.

I have really spent quite some time on this now - i cant imagine that its not possible to get this to work??

My workaround at the moment:

Leaving foo.A to be transient, specifying accessor-type FIELD for bar.B (which gets me property 'x' without problems) and mapping the extra property in B using an annotation in code. But as mentioned before: I would like to solve this completely without annotations - anybody any idea? Blaise? :)

regards,

--qu

回答1:

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.

You appear to have hit a bug. You can track our progress on this issue at the following link. I have provided additional details on this issue below:

https://bugs.eclipse.org/367886

Using Annotations

If you were going to map this use case with JAXB/MOXy annotations you could set @XmlAccessorType(XmlAccessType.NONE) on the A class and do something like:

package forum8727402;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.NONE)
public abstract class A {

    public abstract String getX();

}

package forum8727402;

import javax.xml.bind.annotation.*;    
import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement
public class B extends A {

    @XmlPath("a/b/c/text()")
    private String x;

    public B() {
        x = "Hello World";
    }

    @Override
    public String getX() {
        return x;
    }

    @XmlElement
    public String getCalculatedValue() {
        return "Calculated Value";
    }

}

Demo

package forum8727402;

import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(B.class);

        B b = new B();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(b, System.out);
    }

}

Output

<?xml version="1.0" encoding="UTF-8"?>
<b>
   <a>
      <b>
         <c>Hello World</c>
      </b>
   </a>
   <calculatedValue>Calculated Value</calculatedValue>
</b>

Using MOXy's External Mapping File

oxm.xml

Below is a MOXy external mapping file that represents the equivalent of the previously shown annotations:

<?xml version="1.0" encoding="UTF-8"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum8727402">
    <java-types>
        <java-type name="A" xml-accessor-type="NONE"/>
        <java-type name="B">
            <xml-root-element/>
            <java-attributes>
                <xml-element java-attribute="x" xml-path="a/b/c/text()"/>
                <xml-element java-attribute="calculatedValue"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

Demo

The code below demonstrates how to reference the mapping file:

package forum8727402;

import java.util.*;
import javax.xml.bind.*;    
import org.eclipse.persistence.jaxb.JAXBContextFactory;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(1);
        properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, "forum8727402/oxm.xml");
        JAXBContext jc = JAXBContext.newInstance(new Class[] {A.class, B.class}, properties);

        B b = new B();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(b, System.out);
    }

}

Output

[EL Warning]: 2012-01-04 14:45:46.366--Ignoring attribute [x] on class [forum8727402.xml.B] as no Property was generated for it.
<?xml version="1.0" encoding="UTF-8"?>
<b>
   <calculatedValue>Calculated Value</calculatedValue>
</b>

来源：https://stackoverflow.com/questions/8727402/jaxb-eclipselink-mapping-abstract-getter-to-xml

标签

jaxb

eclipselink

abstract

moxy

oxm