public static void writeToSdCard(String s) {
    try {
      File dst = new File("/sdcard/test_sensor/" + mName + ".txt");
      File parent = dst.getParentFile();
      if(!parent.exists()) {
        parent.mkdirs();
      }
      FileOutputStream outStream = new FileOutputStream(dst, true);
      OutputStreamWriter writer = new OutputStreamWriter(outStream, "gb2312");
      writer.write(s);
      writer.write("\n");
      writer.flush();
      writer.close();// 记得关闭
      outStream.close();
    } catch (Exception e) {
      Log.i("test result", "file write error");
      e.printStackTrace();
    }
}