Transformer not appending Text

// Prepare the DOM document for writing
                Source source = new DOMSource(doc);

                // Prepare the output file
                File file = new File(filename);
                Result result = new StreamResult(file);

                // Write the DOM document to the file
                Transformer xformer = TransformerFactory.newInstance().newTransformer();
                xformer.transform(source, result);

File file = new File(filename);
// true indicates that we want to append to the file
FileOutputStream os = new FileOutputStream (file, true);
Result result = new StreamResult(os);