如何在设备的内部存储中保存文件

Question

我将从浏览器下载文件并存储在设备的内部存储中，路径显示为 /data/data/com.example/files/downloads/sample.pdf 但是第二天我将文件路径视为空“”

使用以下代码从浏览器保存文件：

    private String downloadfile(Uri uri) {
        int count;
        String fileName = "";
        try {
            // Output stream to write file
            String root = null;
//          if (Environment.isExternalStorageRemovable())

//          else
                root = getFilesDir().toString()+ "/download/";

            File file = new File(root);
            if (!file.exists())
                file.mkdirs();
            fileName = file.getAbsolutePath();

            file = new File("" + uri);
            fileName = fileName + "/" + file.getName();

            URL url = new URL(uri.toString());
            URLConnection conection = url.openConnection();
            conection.setRequestProperty("Content-Type",
                    "application/octet-stream");
            conection.setRequestProperty("Expect", "100-continue");
            conection.setRequestProperty("Content-Disposition", "attachment");
            conection.setRequestProperty("filename", file.getName());
            conection.connect();

            // input stream to read file - with 8k buffer
            InputStream input = new BufferedInputStream(url.openStream(), 8192);

            OutputStream output = new FileOutputStream(fileName);
            file = new File(fileName);
            file.createNewFile();
            byte data[] = new byte[1024];

            while ((count = input.read(data)) != -1) {
                output.write(data, 0, count);
            }

            // flushing output
            output.flush();

            // closing streams
            output.close();
            input.close();

        } catch (Exception e) {
            Log.e("Error: ", e.getMessage());
            String inputs = "EX";
            Parameter.trackApplication(inputs, e.getMessage());
            e.printStackTrace();
        }
        return fileName;
    }

我如何解决这个问题，请在我出错的地方纠正我并帮助我解决这个问题。