ApiAsync.java

import android.os.AsyncTask;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by hdias on 07/10/16.
 *
 */
public class ApiAsync extends AsyncTask<String, Void, String> {

    private static final int TIMEOUT_EM_MILISEGUNDOS = 50000;
    private static final String METODO_HTTP_GET = "GET";
    private static final String METODO_HTTP_POST = "POST";

    @Override
    protected String doInBackground(String... params) {
        String endereco = params[0];
        InputStream is = null;
        try {
            URL url = new URL(endereco);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(TIMEOUT_EM_MILISEGUNDOS);
            conn.setConnectTimeout(TIMEOUT_EM_MILISEGUNDOS);
            conn.setRequestMethod(METODO_HTTP_GET);
            conn.setDoInput(true);

            //Adicionar cabeçalho
            //conn.setRequestProperty(HEADER_EMITENTE, emitente);
            conn.setChunkedStreamingMode(1024);

            conn.connect();
            int response = conn.getResponseCode();
            is = conn.getInputStream();
            return readIt(is);
        } catch (Exception ex){
            ex.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return null;
    }

    public String readIt(InputStream stream) throws IOException, UnsupportedEncodingException {
        BufferedReader r = new BufferedReader(new InputStreamReader(stream));
        StringBuilder total = new StringBuilder();
        String line;
        while ((line = r.readLine()) != null) {
            total.append(line);
        }
        return total.toString();
    }

}

gistfile2.txt

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

Main.java

class APi extends ApiAsync{
        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
            builder.setTitle("Recebido");
            builder.setMessage(s);
            builder.setCancelable(true);
            AlertDialog alerta = builder.create();
            alerta.show();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        new APi().execute("http://192.168.0.38:5000/");
    }
}