Salvar .txt Android

WriteAndroid.java

   public class Write {
    public static void writeToFile(String data)throws IOException {
        FileOutputStream stream = null;
        try {
            File root = android.os.Environment.getExternalStorageDirectory();
            File dir = new File(root.getAbsolutePath() + "/UBI");
            dir.mkdirs();
            File file = new File(dir, "LOG_GATEWAY.txt");
            stream = new FileOutputStream(file, true);
             stream.write(data.getBytes());

        } finally {
            if(null != stream){
                stream.close();
            }
        }
    }
  }