public static void main(String argv[]) {

  try {

    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

    // root elements
    Document doc = docBuilder.newDocument();
    Element rootElement = doc.createElement("heroes_data");
    doc.appendChild(rootElement);

    // staff elements
    Element staff = doc.createElement("hero");
    rootElement.appendChild(staff);

    // set attribute to staff element
    //Attr attr = doc.createAttribute("id");
    //attr.setValue("1");
    //staff.setAttributeNode(attr);

    // shorten way
    // staff.setAttribute("id", "1");

    // firstname elements
    Element firstname = doc.createElement("firstname");
    firstname.appendChild(doc.createTextNode("artem"));
    staff.appendChild(firstname);

    // age elements
    Element salary = doc.createElement("age");
    salary.appendChild(doc.createTextNode("18"));
    staff.appendChild(salary);

    // write the content into xml file
    TransformerFactory transformerFactory = TransformerFactory.newInstance();
    Transformer transformer = transformerFactory.newTransformer();
    DOMSource source = new DOMSource(doc);

    //StreamResult result = new StreamResult(new File("C:\file.xml"));

    // Output to console for testing

    StringWriter writer = new StringWriter();
    StreamResult result = new StreamResult(writer);
    transformer.transform(source, result);
    String strResult = writer.toString();

    FileOutputStream out=new FileOutputStream("base");
    BufferedOutputStream bos = new BufferedOutputStream(out);
    // перевод строки в байты
    byte[] buffer = strResult.getBytes();
    bos.write(buffer, 0, buffer.length);
    out.close();

    System.out.println(strResult);

  } catch (ParserConfigurationException pce) {
    pce.printStackTrace();
  } catch (TransformerException tfe) {
    tfe.printStackTrace();
  } catch (IOException ex) {
    ex.printStackTrace();
    //System.out.println(ex.getMessage());
  }
}