XML Tool is a Java library to help developers using XML document. You can build new documents, load existing documents, and execute all sorts of operations onto: delete, renaming, adding tags, attributes, text, data, namespaces, ... Navigation by XPath is also supported.
Since it uses the Fluent Interface pattern, you don't have to know about plenty of classes, but just one: XMLDoc. From there, you can just use your IDE's code completion to check for available methods and call them consecutively.
Here is an excerpt of an example:
XMLDocument doc = XMLDoc.newDocument()
You can download / checkout XML Tool from http://code.google.com/p/xmltool/