This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Edit: Also, remember that the code you have is meant to represent arbitrary JSON data in XML, not to represent arbitrary XML data in JSON. So the test you should apply is whether it converts JSON data to XML accurately.
Ah, yes. I understand the string conversion problem. I haven't used that particular library, so I can't give you a specific solution, but most JSON converters will have a means to control the conversion mapping. I'd dig into the docs to find out how to do it with your library.