XML読み込み＆書き出し

DocumentBuilderFactory dbfactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = dbfactory.newDocumentBuilder();

ByteArrayInputStream bai = new ByteArrayInputStream(buf);
BufferedReader reader = new BufferedReader(new InputStreamReader(bai, "UTF-8"));

Document doc = builder.parse(new InputSource(reader));

/* DO SOMETING */

TransformerFactory transFactory = TransformerFactory.newInstance();
Transformer transformer = transFactory.newTransformer();

DOMSource source = new DOMSource(doc);
ByteArrayOutputStream bao = new ByteArrayOutputStream();
StreamResult result = new StreamResult(bao);
transformer.transform(source, result);