Question

我正在开发一个Android应用程序，我想从服务器下载多个图像并将其存储在SD卡上。哪个是执行此任务的最佳方法。我想在应用程序的后台执行此任务。

Answer 1

使用异步任务将图像下载并保存到外部存储。

class DownloadFileFromURL extends AsyncTask<String, String, String> {

/**
 * Before starting background thread
 * */
@Override
protected void onPreExecute() {
    super.onPreExecute();
    System.out.println("Starting download");
}

/**
 * Downloading file in background thread
 * */
@Override
protected String doInBackground(String... f_url) {
    int count;
    try {
        String root = Environment.getExternalStorageDirectory().toString();

        System.out.println("Downloading");
        URL url = new URL(f_url[0]);

        URLConnection conection = url.openConnection();
        conection.connect();
        // getting file length
        int lenghtOfFile = conection.getContentLength();

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

        // Output stream to write file

        OutputStream output = new FileOutputStream(root+"/downloadedfile.jpg");
        byte data[] = new byte[1024];

        long total = 0;
         while ((count = input.read(data)) != -1) {
                total += count;

               // writing data to file
                output.write(data, 0, count);

             }

           // flushing output
            output.flush();

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

        } catch (Exception e) {
          Log.e("Error: ", e.getMessage());
        }

        return null;
      }



     /**
     * After completing background task
     * **/
    @Override
    protected void onPostExecute(String file_url) {
      System.out.println("Downloaded");
     }
    }

您只需使用

调用上述类

    new DownloadFileFromURL().execute(<The url you want to download from>);

您还需要向Manifest文件添加以下权限

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

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

希望有所帮助

从服务器下载图像并将其存储在SD卡上

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