JAXB Marshal Field that is a subclass

I have a wrapper class with a property whose type is a superclass of several subclasses. I want to marshal to JSON and have the subclass marshalled for that field. When I do it, I get error:

java.lang.IllegalStateException: Invalid JSON namespace: http://www.w3.org/2001/XMLSchema-instance

Specifically, I have a "Wrapper" class with a "result" field of type SuperClass but it will always be an instance of some sub class ("SubClass" below). If I make my Wrapper class have its "result" field defined as subclass type "SubClass" it works OK, but when it is of type "SuperClass" but the instance of of SubClass I get the error.开发者_开发百科

Is there an annotation that I can use here? Do I have to do some sort of custom marshaller?

public class JsonText {

    @XmlRootElement
    public static class SuperClass {
    }

    @XmlRootElement
    public static class SubClass extends SuperClass {
        private int val;
        public int getVal() {return val; }
        public void setVal(int i) {
            val = i;
        }
    }

    @XmlRootElement
     public static class ErrorMessage {
        private String msg;
        public String getMsg() { return msg; }
        public void setMsg(String s) { msg = s;}
    }

    @XmlRootElement
    public static class Wrapper {
        private SuperClass result;
        private ErrorMessage error;
        public SuperClass getResult() { return result; }
        public void setResult(SuperClass sc) { result = sc; }
        public ErrorMessage getError() { return error; }
        public void setError(ErrorMessage e) { error = e; }
    }


    public static void main(String[] args) throws Exception{
        ErrorMessage err = new ErrorMessage();
        err.setMsg("my error");

        SubClass sc = new SubClass();
        sc.setVal(1);

        Wrapper wrapper = new Wrapper();
        wrapper.setResult(sc);
        wrapper.setError(err);

        JAXBContext jc = JAXBContext.newInstance(SuperClass.class, SubClass.class, Wrapper.class);

        Configuration config = new Configuration();
        MappedNamespaceConvention con = new MappedNamespaceConvention config);
        StringWriter writer = new StringWriter();
        XMLStreamWriter xmlStreamWriter = new MappedXMLStreamWriter(con, writer);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.marshal(wrapper, xmlStreamWriter);

        System.out.println(writer.toString());

    }
}