Is it possible to customize the namespace prefix that JAXB uses when marshalling to a String?

Question

http://hwellmann.blogspot.com/2011/03/jaxb-marshalling-with-custom-namespace.html

This shows how to do it.

Another: http://www.systemmobile.com/?p=280

Key bits in case that link dies too:

the NamespacePrefixMapper class, found in the com.sun.xml.bind.marshaller package. The abstract class has one method to implement:

public abstract String getPreferredPrefix(  
     String namespaceUri,         
     String suggestion,         
     boolean requirePrefix); 

then

Marshaller marshaller =        
    jaxbContext.createMarshaller();        
marshaller.setProperty(”com.sun.xml.bind.namespacePrefixMapper”,        
    new MyNamespacePrefixMapper());  

If you’re also using javax.xml.xpath.XPath, your NamespacePrefixMapper can also implement javax.xml.namespace.NamespaceContext, centralizing your namespace customization in a single class.

I tested that in Java SE6 and it requires a small change compared to the solution for Java SE 5 (as described above):

    Marshaller m = context.createMarshaller();
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE );
    m.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
    m.setProperty("com.sun.xml.internal.bind.namespacePrefixMapper", mapper);

So the third property from above contains the additional .internal. in the package name compared to the Java SE5 version. What I did not find out yet is how to tell the Marshaller which namespace URI becomes the default namespace (""). If I override the method getPreferredPrefix() and return an empty string, the Marshaller has issues with writing attributes of the default namespace (in this case it creates a new namespace called ns1)

I had the same question. In package-info.java (if you don't have it, you can just manually create it) add the xmlns part:

@javax.xml.bind.annotation.XmlSchema(xmlns = {
        @javax.xml.bind.annotation.XmlNs(namespaceURI = "urn:just:attributes", prefix = "thirdpartyns") }, 
        elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED)