No response from HTTP GET code when put in Android Activity

Question

I'm trying to write an app that involves an activity that sends a GET request to a webpage, gets the code as a response and then parses it for one specific string (the winner's name). This works just fine when I run it as a stand-alone Java code on my terminal. Putting it into an Android activity though yields no results: neither success nor errors.

Given below is the code of the MainActivity:

package com.projects.appbrewers.swaghrwtracker;

package com.example.myprojects.myapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MainActivity extends AppCompatActivity {

    private final String USER_AGENT = "Mozilla/5.0";
    String url = "<some URL here>";
    String currentWinnerName = "";

    TextView currentWinnerLabel;

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

        currentWinnerLabel = (TextView)findViewById(R.id.currentWinnerLabel);
        currentWinnerLabel.setText("Finding...");
        try
        {
            checkCurrentWinner();
        }
        catch (Exception e)
        {
            //print e.getMessage() to log
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    //HTTP GET Request to Swagbucks HRW iframe page
    public void checkCurrentWinner() throws Exception
    {
        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();

        // optional default is GET
        con.setRequestMethod("GET");

        //add request header
        con.setRequestProperty("User-Agent", USER_AGENT);

        int responseCode = con.getResponseCode();

        if(responseCode == 200)
        {
            BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
            String inputLine;
            StringBuffer response = new StringBuffer();

            while ((inputLine = in.readLine()) != null)
            {
                response.append(inputLine);
            }
            in.close();

            // strip out your required data with a regex
            Pattern pattern = Pattern.compile(".*<div id=\"randomWinnerName\">([a-z0-9]*)</div>.*");
            Matcher matcher = pattern.matcher(response.toString());

            if (matcher.find())
            {
                currentWinnerName = matcher.group(1);
                currentWinnerLabel.setText(currentWinnerName);
            }
            else
                currentWinnerLabel.setText("Not Found!");
        }
        else
            currentWinnerLabel.setText("ERROR!");
    }
}

Answer 1

Here are two options to do it: 1. Use an AsyncTask to perform the HTTP GET operation

private class CheckUsernameFromUrlTask extends AsyncTask<URL, Integer, String> {
     protected String doInBackground(URL... urlToGetTheUsername) {
         String usernameFromHttpGetMethod = null;
         // code to make (similar to your checkCurrentWinner method)
         //   1. HTTP GET request
         //   2. Extract username (incl. error handling)
         return usernameFromHttpGetMethod;
     }

     protected void onProgressUpdate(Integer... progress) {
         // ignore for now, unless you want to show the progress blocking UI
     }

     protected void onPostExecute(String result) {
         // back in the UI thread. Perform all view operations
         // Handle exceptions by saving the exception thrown in 
         // doInBackground method as an instance variable of this class or
         // changing the return object to be a custom object containing
         // username and exception.
         String labelText = result == null ? "Not Found!" : result;
         currentWinnerLabel.setText(labelText );
     }
 }

Then to use the AsyncTask

@Override
protected void onCreate(Bundle savedInstanceState) {
   // ...
   new CheckUsernameFromUrlTask ().execute(url1, url2, url3);
}

2. Use the retrofit library. The library uses a Callback object to get the request asynchronously via a background thread, so you don't have to write code for an AsyncTask. See the documentation for retrofit for examples.