I need to process an XML DOM, preferably with JDOM, where I can do XPath search on nodes. I know the node names or paths, but I want to ignore namespaces completely<
You can use /*:foo (XPath 2.0 or higher) or /yournamespace:* as explained here.
The first variant selects all nodes with the matching name, regardless of what namespace they belong to, including having no namespace. The latter selects all nodes belonging to a specific namespace, regardless of the node name.