Android Studio: Get a connection to a URL

Question

I am having a little bit of trouble getting JSON to load in my project.

I used this getJSON method listed in the answers but it won't work. I figured out that simply the connect() function is throwing a RuntimeException.

Here is my whole class including the getJSON method from another question:

private class GetUnis extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        HttpsURLConnection con = null;
        try {
            URL u = new URL(URL2);
            con = (HttpsURLConnection) u.openConnection();

            con.connect();


            BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line + "\n");
            }
            br.close();

            test = sb.toString();


        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            if (con != null) {
                try {
                    con.disconnect();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
        return null;
    }
}

And I am calling it like this: new GetUnis().execute();

Edit: Here is the StackTrace

java.lang.RuntimeException: An error occured while executing doInBackground()
                                                                                   at android.os.AsyncTask$3.done(AsyncTask.java:304)
                                                                                   at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
                                                                                   at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
                                                                                   at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                                                   at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
                                                                                   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                                                                                   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                                                                                   at java.lang.Thread.run(Thread.java:818)
                                                                                Caused by: java.lang.ClassCastException: com.android.okhttp.internal.http.HttpURLConnectionImpl cannot be cast to javax.net.ssl.HttpsURLConnection
                                                                                   at com.example.lukaskohl.myapplication.SelectUni$GetUnis.doInBackground(SelectUni.java:138)
                                                                                   at com.example.lukaskohl.myapplication.SelectUni$GetUnis.doInBackground(SelectUni.java:131)
                                                                                   at android.os.AsyncTask$2.call(AsyncTask.java:292)
                                                                                   at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                                                   at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
                                                                                   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
                                                                                   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
                                                                                   at java.lang.Thread.run(Thread.java:818)

why not using Retrofit2, It will be easier to code and to read — Faruk, Oct 12 '17 at 18:00
did you set the permission to internet in both manifest and app settings? — Moshe Edri, Oct 12 '17 at 18:38
that is your problem then , go to settings => apps => your app =>permissions — Moshe Edri, Oct 12 '17 at 18:47
Do you mean on the actual phone? Running it on a simulator and there in settings its enabled — Lukas Köhl, Oct 12 '17 at 18:50

Moshe Edri · Accepted Answer · 2017-10-12T18:52:10.233

You can call it from you ui thread you need to do this in a background thread

Basically create an asynctask and move your logic to connect to there

use this code to get the json response as string:

/**
     * This method returns the entire result from the HTTP response.
     *
     * @param url The URL to fetch the HTTP response from.
     * @return The contents of the HTTP response.
     * @throws IOException Related to network and stream reading
     */
    public static String getResponseFromHttpUrl(URL url) throws IOException {
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        try {
            InputStream in = urlConnection.getInputStream();

            Scanner scanner = new Scanner(in);
            scanner.useDelimiter("\\A");

            boolean hasInput = scanner.hasNext();
            if (hasInput) {
                return scanner.next();
            } else {
                return null;
            }
        } finally {
            urlConnection.disconnect();
        }
    }

this one is to check internet connection and will help you avoid calling this task when the user is offline

  public static boolean isNetworkAvaliable(Context ctx) {
        ConnectivityManager connectivityManager = (ConnectivityManager) ctx
                .getSystemService(Context.CONNECTIVITY_SERVICE);
       return  ((connectivityManager
                .getNetworkInfo(ConnectivityManager.TYPE_MOBILE) != null && connectivityManager
                .getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.CONNECTED)
                || (connectivityManager
                .getNetworkInfo(ConnectivityManager.TYPE_WIFI) != null && connectivityManager
                .getNetworkInfo(ConnectivityManager.TYPE_WIFI)
                .getState() == NetworkInfo.State.CONNECTED)) ;
    }








    private class GetUnits extends AsyncTask<URL, Void, String> {


        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(URL... params) {
            URL Url = params[0];

            String searchResults = null;
            try {
                searchResults =getResponseFromHttpUrl(Url);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if(searchResults!=null){
                try {
                    JSONArray unitsArray = new  JSONArray(searchResults);
                    // do something cool with units
//// TODO: 02/08/2017  
                }catch (Exception e){
                    e.printStackTrace();
                    Log.e("Places","error "+e);
                }

            return searchResults;
        }

        @Override
        protected void onPostExecute(String searchResults) {



        }
    }

'.getNetworkInfo(ConnectivityManager.TYPE_MOBILE) != null && connectivityManager'. this line throws a RuntimeException. Also .getNetworkInfo is deprecated. — Lukas Köhl, Oct 12 '17 at 18:30
I get true return value. The other functions also throws an Exception at the line: InputStream in = urlConnection.getInputStream(); — Lukas Köhl, Oct 12 '17 at 18:37
what is URL 2? you need to pass in the URL or build it on spot — Moshe Edri, Oct 12 '17 at 18:41
URL2 is the actual string of the URL. I build the real URL before passing it to getResponseFromHttpUrl — Lukas Köhl, Oct 12 '17 at 18:42
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/156588/discussion-between-moshe-edri-and-lukas-kohl). — Moshe Edri, Oct 12 '17 at 18:52

JAAD · Answer 2 · 2017-10-12T18:46:19.543

0

You are casting it wrong either cast both to javax.net.ssl.HttpsURLConnection or com.android.okhttp.internal.http.HttpURLConnectionImpl

  con = (HttpsURLConnection) u.openConnection();

edited Oct 12 '17 at 18:46

answered Oct 12 '17 at 18:25

JAAD

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This was just debug code. If the connect() was left out it did work. – Lukas Köhl Oct 12 '17 at 18:27
post the new exception then what you exactly get when you dont use debug code – JAAD Oct 12 '17 at 18:31

Android Studio: Get a connection to a URL

2 Answers2