J2SE 5 now includes a javax.xml.namespace.QName class, which allows a prefix to be specified (which is an alias for the namespace). This class has in fact existed for several years in WAS and used by under Sun JSRs 67 ( SAAJ ) and 101 (JAX-RPC 1.0). The original version of QName didn't have a prefix member variable or associated get/set methods.
 
The problem we now face is that WSDL4J is widely used as a component within other middleware products and components so there are serialized QName objects around that don't have a prefix field.
 
If these are deserialized under J2SE 5.0 the prefix field will be ignored - i.e. left as null, which doesn't comply with the QName javadoc for J2SE 1.5 which says default should be "".