HTTPのGETでDataを取得して、Progressバーを表示する

AndroidManifest.xml

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

AndroidManifest.xml

 <ProgressBar
        style="?android:attr/progressBarStyleLarge"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/progress"
        android:max="100"
        android:visibility="gone"
        />
    <Button
        android:layout_marginTop="50dp"
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="btn_onClick"
        android:text="キャンセル"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/txtResult"/>

MainActivity.java

public class MainActivity extends AppCompatActivity {
    AsyncNetworkTask task;

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

        task = new AsyncNetworkTask(this);
        task.execute("http://www.wings.msn.to/");
    }

    public void btn_onClick(View view){
        task.cancel(true);
    }
}

AsyncNetworkTask.java

public class AsyncNetworkTask extends AsyncTask<String, Integer, String>{
    private TextView txtResult;
    private ProgressBar progress;

    public AsyncNetworkTask(Context context){
        super();
        MainActivity activity = (MainActivity)context;
        txtResult = (TextView)activity.findViewById(R.id.txtResult);
        progress = (ProgressBar)activity.findViewById(R.id.progress);
    }

    @Override
    protected void onPreExecute() {
        progress.setVisibility(ProgressBar.VISIBLE);
    }

    @Override
    protected String doInBackground(String... params) {
        publishProgress(30);
        SystemClock.sleep(3000);
        publishProgress(60);
        StringBuilder builder = new StringBuilder();

        try {
            URL url = new URL(params[0]);
            HttpURLConnection con = (HttpURLConnection) url.openConnection();
            con.setRequestMethod("GET");
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(con.getInputStream(), "Shift-JIS"));
            String line;
            while((line = reader.readLine()) != null) {
                builder.append(line);
            }


        } catch (IOException e) {
            e.printStackTrace();
        }

        publishProgress(100);
        return builder.toString();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        Log.d("url", values[0].toString());
    }

    @Override
    protected void onPostExecute(String s) {
        txtResult.setText(s);
        progress.setVisibility(ProgressBar.GONE);
    }

    @Override
    protected void onCancelled() {
        txtResult.setText("キャンセルされました");
        progress.setVisibility(ProgressBar.GONE);
    }
}