JAXB inheritance - unmarshalling to subtypes declared in annotations?

Question

I'd like to unmarshall JAXB beans into subclasses, based on attribute value.

MOXy can do that:

@XmlDiscriminatorNode("@type")
public static class ActionDef extends ContainerOfStackableDefs { ... }

@XmlDiscriminatorValue("cli")
public static class CliActionDef extends ActionDef {
    /** CLI command. EL. */
    @XmlAttribute public String command;
}

However, the JAXBContext needs all the classes specified. Which is kind of unpleasant to define somewhere else than in the "root" class.

I was hoping for something like:

@XmlDiscriminatorNode("@type")
@XmlSubClasses({ CliActionDef.class, XsltActionDef.class, ... })
public static class ActionDef extends ContainerOfStackableDefs { ... }

I don't want to get into XmlAdapters, this is a trivial task and should have trivial solution.

Is there something, either spec or MOXy extension, I could use to simply list the subclasses in the root class?

Otherwise, I'm about to use Jandex to find the subclasses automatically. Afterall, MOXy could do that too ;-)

Update: For the record, then I was getting

Descriptor: XMLDescriptor(org.jboss.loom.migrators._ext.MigratorDefinition$ActionDef --> [])
at org.eclipse.persistence.exceptions.DescriptorException.missingClassIndicatorField(DescriptorException.java:957)
    ...

Which is described here: Exception : "Missing class indicator field from database row [UnmarshalRecordImpl()]." when unmarshalling XML using EclipseLink JAXB (MOXy)

In short: Don't have MOXy unmarshalling to the same-named property as is the name in @XmlDiscriminatorNode("@name"). If you do, then have it @XmlReadOnly and don't have the class abstract.

Update: I still can't get it work. I keep getting the base class. Processed by MOXy, not JDK's impl.

My code:

    <action type="xslt" var="addAction" ...>
    </action>

    <action type="manual">
        ...
    </action>

Beans:

//@XmlRootElement
@XmlDiscriminatorNode("@type")
@XmlSeeAlso({ CliActionDef.class, ModuleActionDef.class, CopyActionDef.class, XsltActionDef.class })
public static class ActionDef extends ContainerOfStackableDefs {
    //@XmlAttribute
    //@XmlReadOnly
    public String typeVal; // Was type, caused an exception.

    //public List<PropertyBean> properties;
    //@XmlAnyAttribute
    public Map<String, String> attribs = new HashMap();
}

@XmlRootElement
@XmlDiscriminatorValue("manual")
public static class ManualActionDef extends ActionDef {
}

public static class FileBasedActionDef extends ActionDef {
    /** Path mask. Ant-like wildcards, EL. */
    @XmlAttribute public String pathMask;

    /** Where to store the result. May be a dir or a file. EL. */
    @XmlAttribute public String dest;
}

@XmlRootElement
@XmlDiscriminatorValue("xslt")
public static class XsltActionDef extends FileBasedActionDef {
    /** XSLT template path. */
    @XmlAttribute public String xslt;
}

What's wrong?

Update:

After putting @XmlDiscriminatorNode("@type") to the top-most class ContainerOfStackableDefs, I get:

Exception Description: Missing class for indicator field value [manual] of type [class java.lang.String].
Descriptor: XMLDescriptor(org.jboss.loom.migrators._ext.MigratorDefinition$ActionDef --> [])
at org.eclipse.persistence.exceptions.DescriptorException.missingClassForIndicatorFieldValue(DescriptorException.java:938)
at org.eclipse.persistence.internal.oxm.QNameInheritancePolicy.classFromRow(QNameInheritancePolicy.java:264)

In short: Missing java.lang.String. :-o Solvable?

Also, I created a simplest test case:

public class JaxbInheritanceTest {    
    @Test
    public void testUnmarshall() throws JAXBException{
        final Unmarshaller marshaller = XmlUtils.createJaxbContext(Root.class).createUnmarshaller();
        Root root = (Root) marshaller.unmarshal( new StringReader(
                "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<root><sub disc=\"foo\"/><sub disc=\"bar\"/></root>") );

        boolean rightClass = (DiscFoo.class.isAssignableFrom( root.subs.get(0).getClass() ));
        Assert.assertTrue( "base elements go into subclasses", rightClass );

        rightClass = (DiscBar.class.isAssignableFrom( root.subs.get(1).getClass() ));
        Assert.assertTrue( "base elements go into subclasses", rightClass );
    }

    @XmlRootElement
    public static class Root {
        @XmlElement(name = "sub")
        List<Base> subs;
    }

    @XmlDiscriminatorNode("@disc")
    @XmlSeeAlso({DiscFoo.class, DiscBar.class})
    public static abstract class Base {}

    @XmlRootElement @XmlDiscriminatorValue("foo")
    public static class DiscFoo {}

    @XmlRootElement @XmlDiscriminatorValue("bar")
    public static class DiscBar {}

}

But this also gives me 2x Base. It's handled by MOXy - checked in debugger.
What's wrong here?

bdoughan bdoughan · Accepted Answer · 2013-07-03T16:52:44

You can use the @XmlSeeAlso (javax.xml.bind.annotation) annotation for this.

@XmlDiscriminatorNode("@type")
@XmlSeeAlso({ CliActionDef.class, XsltActionDef.class, ... })
public static class ActionDef extends ContainerOfStackableDefs { ... }

UPDATE

The problem you are seeing in your latest updated is caused by the @XmlDescriminatorNode not being placed on the root class in your inheritance hierarchy. When I removed ContainerOfStackableDefs from the inheritance hierarchy using @XmlTransient everything worked fine (see: http://blog.bdoughan.com/2011/06/ignoring-inheritance-with-xmltransient.html).

Demo

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

public class Demo {

    @XmlTransient
    public static class ContainerOfStackableDefs {
    }

    @XmlDiscriminatorNode("@type")
    @XmlSeeAlso({ ManualActionDef.class, FileBasedActionDef.class, XsltActionDef.class })
    public static class ActionDef extends ContainerOfStackableDefs {
        //@XmlAttribute
        //@XmlReadOnly
        public String typeVal; // Was type, caused an exception.

        //public List<PropertyBean> properties;
        //@XmlAnyAttribute
        public Map<String, String> attribs = new HashMap();
    }

    @XmlDiscriminatorValue("manual")
    public static class ManualActionDef extends ActionDef {
    }

    @XmlDiscriminatorValue("fileBased")
    public static class FileBasedActionDef extends ActionDef {
        /** Path mask. Ant-like wildcards, EL. */
        @XmlAttribute public String pathMask;

        /** Where to store the result. May be a dir or a file. EL. */
        @XmlAttribute public String dest;
    }

    @XmlDiscriminatorValue("xslt")
    public static class XsltActionDef extends FileBasedActionDef {
        /** XSLT template path. */
        @XmlAttribute public String xslt;
    }

    @XmlRootElement
    public static class Root {

        @XmlElement(name="actionDef")
        public List<ActionDef> actionDefs;

    }

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

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum17453793/input.xml");
        Root root = (Root) unmarshaller.unmarshal(xml);

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

}

input.xml/Output

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <actionDef type="manual"/>
   <actionDef pathMask="PATH MASK" dest="DEST" type="fileBased"/>
   <actionDef xslt="XSLT" type="xslt"/>
</root>

JAXB inheritance - unmarshalling to subtypes declared in annotations?

1 Answers