Android NetworkOnMainThreadException

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Example

From the documentation:

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged.

Here's an example of a code fragment that may cause that exception:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Uri.Builder builder = new Uri.Builder().scheme("http").authority("www.google.com");
        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;
        URL url;
        try {
            url = new URL(builder.build().toString());
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();
        } catch (IOException e) {
            Log.e("TAG","Connection error", e);
        } finally{
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (final IOException e) {
                    Log.e("TAG", "Error closing stream", e);
                }
            }
        }
    }
}  

Above code will throw NetworkOnMainThreadException for applications targeting Honeycomb SDK (Android v3.0) or higher as the application is trying to perform a network operation on the main thread.

To avoid this exception, your network operations must always run in a background task via an AsyncTask, Thread, IntentService, etc.

private class MyAsyncTask extends AsyncTask<String, Integer, Void> {

    @Override
    protected Void doInBackground(String[] params) {
        Uri.Builder builder = new Uri.Builder().scheme("http").authority("www.google.com");
        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;
        URL url;
        try {
            url = new URL(builder.build().toString());
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();
        } catch (IOException e) {
            Log.e("TAG","Connection error", e);
        } finally{
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (final IOException e) {
                    Log.e("TAG", "Error closing stream", e);
                }
            }
        }

        return null;
    }
} 
OutOfMemoryError