import java.io.File;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Comment;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
public class Main {
public static void main(String[] argv) throws Exception {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
factory.setExpandEntityReferences(false);
Document doc = factory.newDocumentBuilder().parse(new File("filename"));
Element element = doc.getElementById("key1");
element = doc.createElement("root");
doc.appendChild(element);
// Insert a comment in front of the element node
Comment comment = doc.createComment("a comment");
doc.insertBefore(comment, element);
}
}