5.1. Changing prefixes
By default, a JAXB marshaller uses random namespace prefixes (such as ns1, ns2, ...) when it needs to declare new namespace URIs. While this is perfectly valid XML wrt the schema, for human readability, you might want to change them to something that makes more sense.
The JAXB RI defines NamespacePrefixMapper to allow you to do this. See the namespace-prefix sample in the distribution for more details.