private void createXMLStream(BufferedOutputStream outStream, String quantity)
             throws IOException {
  String xmlString;
  xmlString = "<item>\n<description>Widget</description>\n<price>500.0</price>\n" +
    "<quantity>" + quantity + "</quantity></item>";
  InputSource xmlStream = new InputSource(new StringReader(xmlString));

  // Build a validating SAX parser using our schema
  SchemaFactory sf = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
  DefaultHandler defHandler = new DefaultHandler() {
      public void warning(SAXParseException s) throws SAXParseException {throw s;}
      public void error(SAXParseException s) throws SAXParseException {throw s;}
      public void fatalError(SAXParseException s) throws SAXParseException {throw s;}
    };
  StreamSource ss = new StreamSource(new File("schema.xsd"));
  try {
    Schema schema = sf.newSchema(ss);
    SAXParserFactory spf = SAXParserFactory.newInstance();
    spf.setSchema(schema);
    SAXParser saxParser = spf.newSAXParser();
    // To set the custom entity resolver, an XML reader needs to be created
    XMLReader reader = saxParser.getXMLReader(); 
    reader.setEntityResolver(new CustomResolver());
    saxParser.parse(xmlStream, defHandler);
  } catch (ParserConfigurationException x) {
    throw new IOException("Unable to validate XML", x);
  } catch (SAXException x) {
    throw new IOException("Invalid quantity", x);
  }

  // Our XML is valid, proceed
  outStream.write(xmlString.getBytes());
  outStream.flush();
}