向sd卡写数据

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

   public void writeToSdCard() throws IOException {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, permissions, REQUEST_CODE);
        } else {
            if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                String name = et_of_name.getText().toString();
                String content = et_of_content.getText().toString();
                String dir = getExternalFilesDir(null).getAbsolutePath();
                dir = dir + "/" + name;
                FileOutputStream fos = new FileOutputStream(dir);
                fos.write(content.getBytes("utf-8"));
                fos.close();
                Toast.makeText(this, "save to external sdcard", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(this, "without external sdcard", Toast.LENGTH_SHORT).show();
            }
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case REQUEST_CODE:
                if (grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    try {
                        writeToSdCard();
                    } catch (IOException e) {
                        Toast.makeText(this, "failed save to external sdcard", Toast.LENGTH_SHORT).show();
                    }
                } else {
                    Toast.makeText(this, "Write External SDCARD Permission Not Granted", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }