I put together an XSD and used JAXB to generate classes out of it.

Here are my XSDs-

myDoc.xsd :
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns="http://www.mydoc.org"
       targetNamespace="http://www.mydoc.org"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"
       xmlns:mtp="http://www.mytypes.com" elementFormDefault="qualified">

<xs:import namespace="http://www.mytypes.com" schemaLocation="mytypes.xsd" />
<xs:element name="myDoc">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="crap" type="xs:string"/>
      <xs:element ref="mtp:foo"/>
      <xs:element ref="mtp:bar"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

mytypes.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://www.mytypes.com"
       xmlns="http://www.mytypes.com"
       xmlns:tns="http://www.mytypes.com"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"
       attributeFormDefault="qualified" elementFormDefault="qualified">


  <xs:element name="foo" type="tns:Foo"/>
  <xs:element name="bar" type="tns:Bar"/>
  <xs:element name="spam" type="tns:Spam"/>

  <xs:simpleType name="Foo">
    <xs:restriction base="xs:string"></xs:restriction>
  </xs:simpleType>

  <xs:complexType name="Bar">
    <xs:sequence>
      <xs:element ref="spam"/>
    </xs:sequence>
  </xs:complexType>

  <xs:simpleType name="Spam">
    <xs:restriction base="xs:string" />
  </xs:simpleType>

</xs:schema>

The document marshalled is-

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<myDoc xmlns:ns2="http://www.mytypes.com">
  <crap>real crap</crap>
  <ns2:foo>bleh</ns2:foo>
  <ns2:bar>
    <spam>blah</spam>
  </ns2:bar>
</myDoc>

Note that the <spam> element uses the default namespace. I would like it to use the ns2 namespace. The schema (mytypes.xsd) expresses the fact that <spam> is contained within <bar> which in the XML instance is bound to the ns2 namespace.

I've broken my head over this for over a week and I would like ns2 prefix to appear in <spam>. What should I do?

Required :

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<myDoc xmlns:ns2="http://www.mytypes.com">
  <crap>real crap</crap>
  <ns2:foo>bleh</ns2:foo>
  <ns2:bar>
    <ns2:spam>blah</ns2:spam><!--NS NS NS-->
  </ns2:bar>
</myDoc>