MOXy Dynamix JAXB context unmarshalls to wrong property names

Question

Your ADDITION is correct, MOXy isn't unmarshalling wrong property names, it just unmarshals to property names that correspond to what the mapped property/field names would be in the generated classes.

What the Solution Should Be

binding.xml

The default XML Schema to Java naming rules in JAXB is to remove the _. You can supply a binding file to have this behaviour be different.

<jaxb:bindings 
    xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
    version="2.1">
    <jaxb:globalBindings underscoreBinding="asCharInWord"/>
</jaxb:bindings>

Demo

Using MOXy's Dynamic JAXB, below is an example of how you can leverage the bindings file.

import java.io.File;
import java.util.*;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.dynamic.DynamicEntity;
import org.eclipse.persistence.jaxb.dynamic.DynamicJAXBContextFactory;

public class Demo {

    public static void main(String[] args) throws Exception {
        StreamSource schemaSource = new StreamSource("src/forum20146935/schema.xsd");
        Map<String, Object> properties = new HashMap<String, Object>(1);
        properties.put(DynamicJAXBContextFactory.EXTERNAL_BINDINGS_KEY, new StreamSource("src/forum20146935/binding.xml"));
        JAXBContext jc = DynamicJAXBContextFactory.createContextFromXSD(schemaSource, null, Demo.class.getClassLoader(), properties);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum20146935/input.xml");
        DynamicEntity root = (DynamicEntity) unmarshaller.unmarshal(xml);
        System.out.println(root.get("foo_bar"));
    }

}

Why Didn't it Work?

As I mentioned earlier MOXy will base the dynamic property name based on the corresponding mapped field/property generated by XJC. This happens to look something like where the property name has the _ but the corresponding mapped field does not.

@XmlElement(name = "foo_bar", required = true)
protected String fooBar;

public String getFoo_Bar() {
    return fooBar;
}

public void setFoo_Bar(String value) {
    this.fooBar = value;
}

What you Could Do Instead

Use the transformed key name.

You could use the getValueByXPath functionality on the MOXy JAXBContext to interact with the objects in a more XML like way.

import java.io.File;
import java.util.*;

import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;

import org.eclipse.persistence.dynamic.DynamicEntity;
import org.eclipse.persistence.jaxb.JAXBHelper;
import org.eclipse.persistence.jaxb.dynamic.DynamicJAXBContextFactory;

public class Demo {

    public static void main(String[] args) throws Exception {
        StreamSource schemaSource = new StreamSource("src/forum20146935/schema.xsd");
        Map<String, Object> properties = new HashMap<String, Object>(1);
        properties.put(DynamicJAXBContextFactory.EXTERNAL_BINDINGS_KEY, new StreamSource("src/forum20146935/binding.xml"));
        JAXBContext jc = DynamicJAXBContextFactory.createContextFromXSD(schemaSource, null, Demo.class.getClassLoader(), properties);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum20146935/input.xml");
        DynamicEntity root = (DynamicEntity) unmarshaller.unmarshal(xml);

        String fooBar = JAXBHelper.getJAXBContext(jc).getValueByXPath(root, "foo_bar/text()", null, String.class);
        System.out.println(fooBar);
    }

}