java - Adding namespace to an already created XML document

Question

I am creating a W3C Document object using a String value. Once I created the Document object, I want to add a namespace to the root element of this document. Here's my current code:

Document document = builder.parse(new InputSource(new StringReader(xmlString)));
document.getDocumentElement().setAttributeNS("http://com", "xmlns:ns2", "Test");
document.setPrefix("ns2");
TransformerFactory tranFactory = TransformerFactory.newInstance();
Transformer aTransformer = tranFactory.newTransformer();
Source src = new DOMSource(document);
Result dest = new StreamResult(new File("c:\xmlFileName.xml"));
aTransformer.transform(src, dest);

What I use as input:

<product>
    <arg0>DDDDDD</arg0>
    <arg1>DDDD</arg1>
</product>

What the output should look like:

<ns2:product xmlns:ns2="http://com">
    <arg0>DDDDDD</arg0>
    <arg1>DDDD</arg1>
</ns2:product>

I need to add the prefix value and namespace also to the input xml string. If I try the above code I am getting this exception:

NAMESPACE_ERR: An attempt is made to create or change an object in a way which is incorrect with regard to namespaces.

Appreciate your help!

Answer 1

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");