Adding namespace to an already created XML document

Since there is not an easy way to rename the root element, we'll have to replace it with an element that has the correct namespace and attribute, and then copy all the original children into it. Forcing the namespace declaration is not needed because by giving the element the correct namespace (URI) and setting the prefix, the declaration will be automatic.

Replace the setAttribute and setPrefix with this (line 2,3)

String namespace = "http://com";
String prefix = "ns2";
// Upgrade the DOM level 1 to level 2 with the correct namespace
Element originalDocumentElement = document.getDocumentElement();
Element newDocumentElement = document.createElementNS(namespace, originalDocumentElement.getNodeName());
// Set the desired namespace and prefix
newDocumentElement.setPrefix(prefix);
// Copy all children
NodeList list = originalDocumentElement.getChildNodes();
while(list.getLength()!=0) {
    newDocumentElement.appendChild(list.item(0));
}
// Replace the original element
document.replaceChild(newDocumentElement, originalDocumentElement);

In the original code the author tried to declare an element namespace like this:

.setAttributeNS("http://com", "xmlns:ns2", "Test");

The first parameter is the namespace of the attribute, and since it's a namespace attribute it need to have the http://www.w3.org/2000/xmlns/ URI. The declared namespace should come into the 3rd parameter

.setAttributeNS("http://www.w3.org/2000/xmlns/", "xmlns:ns2", "http://com");