Solved Creating XML File

Hello,
To save data in my plugin I want to use an xml file.
I've read the following tutorial on how to create an xml file in Java: http://www.mkyong.com/java/how-to-create-xml-file-in-java-dom/
Now I still have an error I can't get rid of, namely a nullpointerexeption.

I want the following xml setup:

Code:

<world id="world_world">
  <city id="mayor_Jeroen">
  </city>
</world

I run the following code in the "onEnable()":

Code:java

DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
Document doc = docBuilder.newDocument();
 
dataFolder.mkdir();
xmlFile = new File(dataFolder, "save.xml");

Of course, with a try/catch for ParserConfigurationException.

Now the error comes if I want to run the following method:

Code:java

public static void addCity(Player mayor, World world) {
Element city = doc.createElement("city");
if (doc.getElementById("world_" + world.toString()) == null) {
addWorld(world);
}
doc.getElementById("world_" + world.toString()).appendChild(city); // This line is where the nullpointerexception is thrown
city.setAttribute("id", "mayor_" + mayor.getName());
saveToFile();
}

This saveToFile() method contains the following, again with try/catch:

Code:java

TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer();
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(xmlFile);
transformer.transform(source, result);

Now I can't figure out what I am doing wrong...
Can anyone help me?
Thanks in advace,
Jeroen D.

Solved it by using a YML file instead of XML file.
For anyone else needing a tutorial on YML:
http://wiki.bukkit.org/Configuration_API_Reference

EDIT by Moderator: merged posts, please use the edit button instead of double posting.