Connecting to a URL

Question

I want to read the content of a URL with the following code :

        myUrl=new URL(url);
        stream=myUrl.openStream();

but the second line of code triggers an "android.os.NetworkOnMainThreadException" without any other explanation.

I work under Androïd 4 and I can add this code used to work with Androïd 2.3.3.

Any idea?

Thanks in advance for the time you will spend trying to help me.

I think you need to put your code in a separate thread or an AsyncTask. — iTurki, Sep 29 '12 at 13:43
Maybe [this answer](http://stackoverflow.com/a/9415736) would help? — poplitea, Sep 29 '12 at 13:44

score 1 · Accepted Answer · edited May 23 '17 at 12:18

So problem is that application attempts to perform a networking operation on main thread and this is not allowed.

For your goal i recommend to you use AsyncTask and do your work in background Thread.

Here is example from my little app:

protected InputStream doInBackground(String... params) {

            int contentLength = 0;
            int buffLength = 0;
            int progress = 0;
            InputStream inputStream = null;
            try {

                URL url = new URL(params[0]);
                HttpURLConnection urlConntection = (HttpURLConnection) url.openConnection();
                urlConntection.setRequestMethod("GET");
                urlConntection.setAllowUserInteraction(false);
                urlConntection.setInstanceFollowRedirects(true);
                urlConntection.connect();
                if (urlConntection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                    contentLength = urlConntection.getContentLength();
                    progressDialog.setMax(contentLength);
                    inputStream = urlConntection.getInputStream();

                    while ((buffLength = inputStream.read(MAX_BUFFER)) != -1) {
                        try {
                            Thread.sleep(1);
                            progress += buffLength;
                            DataTransmitted data = new DataTransmitted(progress, contentLength);
                            publishProgress(data);
                        }
                        catch (InterruptedException ex) {
                            Log.e(this.getClass().getName(), ex.getMessage());
                        }
                    }

                }
                else {
                    throw new IOException("No response.");
                }

            }
            catch (MalformedURLException ex) {
                Log.e(this.getClass().getName(), ex.getMessage());
            }
            catch (IOException ex) {
                errorDialog.show();
            }
            return inputStream;
        }

Or here is similar topic:

Download a file with Android, and showing the progress in a ProgressDialog

iTurki · Answer 2 · 2012-09-29T13:56:43.190

1

From the Android developer's site:

A NetworkOnMainThreadException is thrown when an application attempts to perform a networking operation on its main thread.

You need to put your code in a separate thread or an AsyncTask.

Android versions 3.0 and above are much stricter about abuse against the UI Thread Read this article for more details

edited Sep 29 '12 at 13:56

answered Sep 29 '12 at 13:46

iTurki

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score 1 · Answer 3 · answered Sep 29 '12 at 14:06

You need to use AsyncTask now here's a quick example, i hope that will help you:

public class SimpleWebGrab extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    grabURL("http://android.com");
}

public void grabURL(String url) {
    new GrabURL().execute(url);
}

private class GrabURL extends AsyncTask<String, Void, Void> {
    private final HttpClient Client = new DefaultHttpClient();
    private String Content;
    private String Error = null;
    private ProgressDialog Dialog = new ProgressDialog(SimpleWebGrab.this);

    protected void onPreExecute() {
        Dialog.setMessage("Downloading source..");
        Dialog.show();
    }

    protected Void doInBackground(String... urls) {
        try {
            HttpGet httpget = new HttpGet(urls[0]);
            ResponseHandler<String> responseHandler = new BasicResponseHandler();
            Content = Client.execute(httpget, responseHandler);
        } catch (ClientProtocolException e) {
            Error = e.getMessage();
            cancel(true);
        } catch (IOException e) {
            Error = e.getMessage();
            cancel(true);
        }

        return null;
    }

    protected void onPostExecute(Void unused) {
        Dialog.dismiss();
        if (Error != null) {
            Toast.makeText(SimpleWebGrab.this, Error, Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(SimpleWebGrab.this, "Source: " + Content, Toast.LENGTH_LONG).show();
        }
    }

}
}

And please : call it Android, not Androïd it sounds french.

Connecting to a URL

3 Answers3