使用 Asynctask 从 Web 服务器下载文本文件

Question

/**
 * Downloading file in background thread
 * */
@Override
protected String doInBackground(String... f_url) {
  int count;
  try {
    String root = Environment.getExternalStorageDirectory().toString(); // "/storage/emulated/0"
    System.out.println("Downloading");
    URL url = new URL(f_url[0]); //http://xxx.168.2.200/tmp/bsp1.txt;
    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(fileNameDaten);
    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) {
    String fel=e.getMessage();
    Log.e("Error: ", e.getMessage());
  }
  return null;
}
/**
 * After completing background task
 * **/
@Override
protected void onPostExecute(String file_url) {
  System.out.println("Downloaded");
}

}

doInBackground is running until "conection.connect();" After about 3 minutes the app will continue with an exception: "Failed to connect to /xxx.168.2.200:80" In principle, I can access the web server's HTML pages with my mobile phone. My question: What does the error message mean and how can I fix the error?

Answer 1

networkSecurityConfig: not added to manifest, how to formulate?

app targets android 9, API 28 only partially installed

I will use the app only for local adresses

Follows manifest: enter code here

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="de.wicki.pdftextapplication">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE" />
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />
<application
    android:usesCleartextTraffic="true"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".UploadToServer"></activity>
    </application>

</manifest>