JAXB Polymorphism of little use

Question

HI all.
I am finding little use in JAXB's polymorphism. As such, I think I'm going to need to switch to another framework that has a more useful polymorphism feature (or else none at all).
As indicated below, I have a schema that includes a "Person" complex type, and an "Employee" complex type that extends it. There is also an element "people" that is a sequence of "Person" elements. I have used JAXB-generated classes to add instances of Person and Employee (generated classes) to an instance of the People class. The marshaller then erroneously outputs the extensions to Person found in Employee (see below).
Having seen this, I wonder what use polymorphism (in the classes generated by JAXB) has, if it is not acceptable to use a subclass wherever its superclass is allowed. Perhaps there is some other way to do polymorphism that I'm missing?
I really want to have a functionality such as the code example below implies. Does JAXB have the feature I'm looking for, or do I need to switch to another framework? If I need to switch, which one should I use?
Thanks for any help that can be offered.
schema:
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
     <xs:element name="people">
          <xs:annotation>
               <xs:documentation>Comment describing your root element</xs:documentation>
          </xs:annotation>
          <xs:complexType>
               <xs:sequence>
                    <xs:element name="person" type="Person" maxOccurs="unbounded"/>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
     <xs:complexType name="Person">
          <xs:sequence>
               <xs:element name="name" type="xs:string"/>
          </xs:sequence>
     </xs:complexType>
     <xs:complexType name="Employee">
          <xs:complexContent>
               <xs:extension base="Person">
                    <xs:sequence>
                         <xs:element name="title" type="xs:string"/>
                    </xs:sequence>
               </xs:extension>
          </xs:complexContent>
     </xs:complexType>
</xs:schema>
expected JAXB output:
<people>
<person>
<name>Joe Sample</name>
</person>
<person>
<name>Jane Sample Employee</name>
</person>
</people>
actual JAXB output (invalid):
<people>
<person>
<name>Joe Sample</name>
</person>
<person>
<name>Jane Sample Employee</name>
<title>Engineer</title>
</person>
</people>
Java code:
Person person = factory.createPerson();
person.setName("Joe Sample");
Employee employee = factory.createEmployee();
employee.setName("Jane Sample Employee");
employee.setTitle("Engineer");
People people = factory.createPeople();
people.getPerson().add(person);
people.getPerson().add(employee);
- Matt Munz

Answer 1

hi Matt,
I think your expected output may be wrong, and the actual output be correct eg consider this code:
import java.util.*;
class Person {
     String name;
     public String toString() { return "Person("+name+")"; } }
class Employee extends Person {
     String title;
     public String toString() { return "Employee("+name+", "+title+")"; } }
public class JBTest {
     public static void main(String[]arg) {
          List l = new ArrayList();
          Person p = new Person();
          p.name="Joe Sample";
          Employee q = new Employee();
          q.name="Jane Sample Employee";
          q.title="Engineer";
          l.add(p);
          l.add(q);
          System.out.println(l);
which outputs
     [Person(Joe Sample), Employee(Jane Sample Employee, Engineer)]
So although the List is untyped (am not keeping up with generics..
sorry!) in the above code, even if it were a Person list it would still be legitimate to add an Employee to the list (since an Employee is-a
Person)
saying that, am not sure how you could achieve what you are trying? are you hoping for the object tree you construct not to be validated?
thanks,
asjf