HTTPUrlConnection crashes app on getOutputStream().write (hanging, no Exception thrown)

Question

I am trying to write a network functionality for an android application with android studio. It is very simple. I just try to post some data to an url and fetch data back (all in simple HTTP). I am testing with the emulator, device is Pixel 2 API 28.

As long as the internet is activated on the emulator everything works fine. But as soon as i disable the wifi, the application hangs when I try to send the data, and finally crashes. Android offers to stop the application.

It hangs on this call:

urlConnection.getOutputStream().write(postDataBytes);

Documentation and web say, that this method should throw an exception, when there is no internet connection. Especially the UnknownHostException is mentioned very often. But I do not receive any exception.

Where could I go from here?

Here is the code of the whole connection class i use. The doInBackground method is the place where the internet magic happens and the error occures:

package com.example.tf2;

//This class is used for easier networking.
//It is using volley..

import android.content.Context;
/* import android.graphics.Bitmap; */
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.util.Log;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.net.UnknownHostException;
import java.util.HashMap;
import java.util.Map;

/* Info about "associative arrays" for the post params taken from Stackoverflow:
https://stackoverflow.com/questions/5122913/java-associative-array
 */

public class mvNetConnect extends AsyncTask<String, Void, String> {
    private final String endpoint = "*** here is a valid url ***";
    Map<String, String> post_params = new HashMap<String, String>();
    String mode = "GET";
    String token = "";
    private Context useContext;

    public mvNetConnect(Context myContext) {
        useContext = myContext;
    }

    @Override
    protected String doInBackground(String... urls) {
        String result = "";
        URL url;
        HttpURLConnection urlConnection;

        try {
            //Daten aus Eingabefeldern auslesen.
            //TextView textview_username =

            url = new URL(endpoint + urls[0]);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setConnectTimeout(1000);     // Timeout in Millisekunden. Ansonsten bekommt der Enduser nie eine Antwort..
            urlConnection.setReadTimeout(1000);


            //Falls wir ein Token haben, fügen wir es dem Request hinzu..
            if(token != "") {
                urlConnection.addRequestProperty("auth", token);
            }

            //Falls dies ein Post-Aufruf ist, machen wir auch einen daraus..
            StringBuilder postData = new StringBuilder();


            if(mode == "POST") {
                urlConnection.setRequestMethod("POST");

                //Post Parameter hinzufügen (Loop taken from stackoverflow (Thread from harto): https://stackoverflow.com/questions/1066589/iterate-through-a-hashmap)
                for (Map.Entry<String, String> entry : post_params.entrySet()) {
                    String key = entry.getKey();
                    String value = entry.getValue();

                    // Add Params to request..
                    if (postData.length() != 0) {
                        postData.append('&');
                    }
                    postData.append(URLEncoder.encode(key, "UTF-8"));
                    postData.append('=');
                    postData.append(URLEncoder.encode(value, "UTF-8"));
                }

                byte[] postDataBytes = postData.toString().getBytes("UTF-8");
                urlConnection.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
                urlConnection.setDoOutput(true);
                urlConnection.getOutputStream().write(postDataBytes);

            }

            InputStream in = urlConnection.getInputStream();
            InputStreamReader reader = new InputStreamReader(in);
            int data = reader.read();       //Erstes Zeichen lesen.

            while(data != -1) {             //So lang es Daten gibt.
                char current = (char) data; //Zeichen umwandeln.
                result += current;          //Zeichen an Ausgabe anhängen.
                data = reader.read();       //Nächstes Zeichen lesen.
            }



        } catch(UnknownHostException e) {
            Log.i("Info", "error!!!");
        } catch(MalformedURLException e) {
            Log.i("Info", "no error?");
            e.printStackTrace();
            return "Failed";
        } catch(Exception e) {
            Log.i("Info", "errors..");
            e.printStackTrace();
            return "Failed";
        } catch (Throwable throwable) {
            // Output unexpected Throwables.
            Log.i("info", throwable.toString());
        }

        Log.i("Info", result.toString());

        return result;
    }

    public void setModeToPost() {
        mode = "POST";
    }

    public void setModeToGet() {
        mode = "GET";
    }

    public void setToken(String _token) {
        token = _token;
    }

    public void addPostParam(String key, String value) {
        post_params.put(key, value);
        //To extract a key one could use: post_params.get(key);
    }

    public void clearPostParams(String key, String value) {
        post_params.clear();
    }
}