https://stackoverflow.com/questions/55018033/error-when-inserting-node-before-another-in-xml

ContentDuplicator.java

public class ContentDuplicator {

    public static void main(String[] args)
            throws IOException, SAXException, ParserConfigurationException, TransformerException {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
                + "<note>\n"
                + "    <content>\n"
                + "        <ele> something </ele>\n"
                + "        <tic> something else </tic>\n"
                + "    </content>\n"
                + "\n"
                + "    <tac>data</tac>\n"
                + "    <toc>data2</toc>\n"
                + "</note>";

        Document document = parseXml(xml);
        Node tacNode = document.getElementsByTagName("tac").item(0);
        Node noteNode = document.getElementsByTagName("note").item(0);
        NodeList contentNode = document.getElementsByTagName("content");
        Node newNode = contentNode.item(0).cloneNode(true);

        noteNode.insertBefore(newNode, tacNode);

        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer = tf.newTransformer();
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        StringWriter writer = new StringWriter();
        transformer.transform(new DOMSource(document), new StreamResult(writer));
        String output = writer.getBuffer().toString();
        System.out.println(output);

    }

    private static Document parseXml(String file)
            throws ParserConfigurationException, IOException, SAXException {
        DocumentBuilderFactory factory =
                DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        ByteArrayInputStream input = new ByteArrayInputStream(file.getBytes(StandardCharsets.UTF_8));
        return builder.parse(input);
    }
}

sample.xml

<?xml version="1.0" encoding="UTF-8"?>
<note>
  <content>
      <ele> something </ele>
      <tic> something else </tic>
  </content>
  <tac>data</tac>
  <toc>data2</toc>
</note>
<content>
  <ele> something </ele>
  <tic> something else </tic>
</content>