Strip whitespace and newlines from XML in Java

Question

Using Java, I would like to take a document in the following format:

Answer 1

Java8+transformer does not create any but Java10+transformer puts everywhere empty lines. I still want to keep a pretty indents. This is my helper function to create xml string from any DOMElement instance such as doc.getDocumentElement() root node.

public static String createXML(Element elem) throws Exception {
        DOMSource source = new DOMSource(elem);
        StringWriter writer = new StringWriter();
        StreamResult result = new StreamResult(writer);
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        //transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
        //transformer.setOutputProperty("http://www.oracle.com/xml/is-standalone", "yes");
        transformer.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC,"yes");
        transformer.setOutputProperty("http://www.oracle.com/xml/is-standalone", "yes");
        transformer.transform(source, result);

        // Java10-transformer adds unecessary empty lines, remove empty lines
        BufferedReader reader = new BufferedReader(new StringReader(writer.toString()));
        StringBuilder buf = new StringBuilder();
        try {
            final String NL = System.getProperty("line.separator", "\r\n");
            String line;
            while( (line=reader.readLine())!=null ) {
                if (!line.trim().isEmpty()) {
                    buf.append(line); 
                    buf.append(NL);
                }
            }
        } finally {
            reader.close();
        }
        return buf.toString();  //writer.toString();
    }