Issues converting Node to Document

Question

I am trying to update an existing method to avoid XXE attack. Below is the existing method:

private String xmlToString(final Node node) {
    try {
        final Source source = new DOMSource(node);
        final StringWriter stringWriter = new StringWriter();
        final Result result = new StreamResult(stringWriter);
        final TransformerFactory factory = TransformerFactory.newInstance();
        final Transformer transformer = factory.newTransformer();
        transformer.transform(source, result);

        return stringWriter.getBuffer().toString();
    } catch (final TransformerConfigurationException e) {
        LOG.error("Unable to convert XML node to string", e);
    } catch (final TransformerException e) {
        LOG.error("Unable to convert XML node to string", e);
    }

    return null;
}

Here is my modification:

private String xmlToString(final Node node) {
    try {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        documentBuilderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
        documentBuilderFactory.setFeature("http://xml.org/sax/features/external-general-entities", false);
        documentBuilderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
        documentBuilderFactory.setNamespaceAware(true);

        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        Document document = documentBuilder.newDocument();
        Node importedNode = document.importNode(node, true);
        document.appendChild(importedNode);             

        final Source source = new DOMSource(document);
        final StringWriter stringWriter = new StringWriter();
        final Result result = new StreamResult(stringWriter);
        final TransformerFactory factory = TransformerFactory.newInstance();
        //factory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
        final Transformer transformer = factory.newTransformer();
        transformer.transform(source, result);

        return stringWriter.getBuffer().toString();
    } catch (final TransformerConfigurationException e) {
        LOG.error("Unable to convert XML node to string", e);
    } catch (final TransformerException e) {
        LOG.error("Unable to convert XML node to string", e);
    } catch (ParserConfigurationException e) {
        LOG.error("Unable to convert XML node to string", e);
    }

    return null;
}

I initially added setFeature property for TransformerFactory (commented line of code) and saw the following error:

java.lang.UnsupportedOperationException: This class does not support JDK1.5
    at weblogic.xml.jaxp.RegistryTransformerFactory.setFeature(RegistryTransformerFactory.java:317)

Then I decided to add DocumentBuilderFactory to the method and convert the node to document. I saw this link and updated my method.

But, I see the below error:

org.w3c.dom.DOMException: NOT_SUPPORTED_ERR: The implementation does not support the requested type of object or operation.
    at org.apache.xerces.dom.CoreDocumentImpl.importNode(Unknown Source)
    at org.apache.xerces.dom.CoreDocumentImpl.importNode(Unknown Source)

Can somebody please help me correcting the problem.

Thanks,

NN.