HttpURLConnection returns errors when calling connect()

Question

I'm new to Android and am trying to pass the String json to an API through httpURLConnection, but it always returns an error. This is a copy of a code that I found online that should work. I tried to create another class that extends AsyncTask, but I don't know how to return the results from the API.Can someone please tell me what I did wrong and help me correct it.

String json = "{\"requests\":[{\"image\":{\"content\":\"" + encodedString +  "\"},\"features\":[{\"type\":\"LABEL_DETECTION\",\"maxResults\":\"10\"}]}]}";

            try{

                URL urlObj = new URL(urlVisit);
                HttpURLConnection conn = (HttpURLConnection) urlObj.openConnection();
                conn.setDoOutput(true);
                conn.setRequestMethod("POST");
                conn.setRequestProperty("Accept-Charset", "UTF-8");
                conn.setReadTimeout(10000);
                conn.setConnectTimeout(15000);
                conn.connect();
                DataOutputStream wr = new DataOutputStream(conn.getOutputStream());
                wr.writeBytes(json);
                wr.flush();
                wr.close();

                InputStream in = new BufferedInputStream(conn.getInputStream());
                BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                StringBuilder result = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }

                Log.d("test", "result from server: " + result.toString());

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

the errors given by the console:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: edmt.dev.androidcamera2api, PID: 22584
android.os.NetworkOnMainThreadException
    at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1460)
    at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:102)
    at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:90)
    at java.net.InetAddress.getAllByName(InetAddress.java:787)
    at com.android.okhttp.Dns$1.lookup(Dns.java:39)
    at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:175)
    at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:141)
    at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:83)
    at com.android.okhttp.internal.http.StreamAllocation.findConnection(StreamAllocation.java:174)
    at com.android.okhttp.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:126)
    at com.android.okhttp.internal.http.StreamAllocation.newStream(StreamAllocation.java:95)
    at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:281)
    at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:224)
    at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:461)
    at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:127)
    at com.android.okhttp.internal.huc.DelegatingHttpsURLConnection.connect(DelegatingHttpsURLConnection.java:89)
    at com.android.okhttp.internal.huc.HttpsURLConnectionImpl.connect(Unknown Source:0)
    at edmt.dev.androidcamera2api.MainActivity$2.onClick(MainActivity.java:177)
    at android.view.View.performClick(View.java:6291)
    at android.view.View$PerformClick.run(View.java:24931)
    at android.os.Handler.handleCallback(Handler.java:808)
    at android.os.Handler.dispatchMessage(Handler.java:101)
    at android.os.Looper.loop(Looper.java:166)
    at android.app.ActivityThread.main(ActivityThread.java:7523)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)

Prokash Sarkar · Accepted Answer · 2019-01-27T07:18:57.320

From your stack trace, you are trying to execute the network call from the MainThread.

E/AndroidRuntime: FATAL EXCEPTION: main
Process: edmt.dev.androidcamera2api, PID: 22584
android.os.NetworkOnMainThreadException

You should wrap your network call inside an AsyncTask or any other background thread that doesn't block the UI.

Here's a code snippet to get you started:

class TestAsync extends AsyncTask<String, Integer, String>
    {

        protected void onPreExecute (){
            super.onPreExecute();
        }

        protected String doInBackground(String... params) {
            // wrap the network call here
            String json = "{\"requests\":[{\"image\":{\"content\":\"" + encodedString +  "\"},\"features\":[{\"type\":\"LABEL_DETECTION\",\"maxResults\":\"10\"}]}]}";

            StringBuilder result = new StringBuilder();

            try{

                URL urlObj = new URL(params[0]);
                HttpURLConnection conn = (HttpURLConnection) urlObj.openConnection();
                conn.setDoOutput(true);
                conn.setRequestMethod("POST");
                conn.setRequestProperty("Accept-Charset", "UTF-8");
                conn.setReadTimeout(10000);
                conn.setConnectTimeout(15000);
                conn.connect();
                DataOutputStream wr = new DataOutputStream(conn.getOutputStream());
                wr.writeBytes(json);
                wr.flush();
                wr.close();

                InputStream in = new BufferedInputStream(conn.getInputStream());
                BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                String line;
                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }

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

            return result.toString();
        }

        protected void onProgressUpdate(Integer...a){
            super.onProgressUpdate(a);
        }

        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            Log.d("test", "result from server: " + result);
        }
    }

To call the AsyncTask:

 new TestAsync().execute(urlVisit);

I'm really sorry. I tried making it work but it doesn't. I'm at a hackathon and we've been working over this for the past 12 hours. Could you specify, or fill the methods for me/us? — Hassan G, Jan 27 '19 at 05:38
I understand that I need to make a AsyncTask thread that doesn't block the main thread UI. However, I need to retrieve the data I get from my network calls and I don't know how to implement that into AsyncTask — Hassan G, Jan 27 '19 at 05:51

score 0 · Answer 2 · answered Jan 27 '19 at 04:59

0

Did you add Internet Permission on AndroidManifest.xml?

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

answered Jan 27 '19 at 04:59

touhid udoy

4,005
2
18
31

yes, i did. The problem is with the asynchronous call – Hassan G Jan 27 '19 at 05:11

HttpURLConnection returns errors when calling connect()

2 Answers2