Tutorial: Push notifications to Android devices by using Azure Notification Hubs and Google Cloud Messaging

04/05/2018
17 minutes to read
Contributors

Overview

This tutorial shows you how to use Azure Notification Hubs to send push notifications to an Android application. You create a blank Android app that receives push notifications by using Google Cloud Messaging (GCM).

Important

This topic demonstrates push notifications with Google Cloud Messaging (GCM). If you are using Google's Firebase Cloud Messaging (FCM), see Sending push notifications to Android with Azure Notification Hubs and FCM.

The completed code for this tutorial can be downloaded from GitHub here.

In this tutorial, you do the following actions:

Create a project that supports Google Cloud Messaging.
Create a notification hub
Connect your app to the notification hub
Test the app

Prerequisites

Azure subscription. If you don't have an Azure subscription, create a free account before you begin.
Android Studio.

Creating a project that supports Google Cloud Messaging

Navigate to the Google Cloud Console, sign in with your Google account credentials.
Select Create Project on the toolbar.
For Project name, enter a name for your project, and click Create.
Select the alerts button on the toolbar, and select your project in the list. You see the dashboard for your project. You can also navigate directly to the dashboard by using the URL: https://console.developers.google.com/home/dashboard?project=
Note down the Project number in the Project info tile of the dashboard.
In the dashboard, on the APIs tile, select Got to APIs overview.
On the API page, select ENABLE APIS AND SERVICES.
Search for and select Google Cloud Messaging.
To enable Google Cloud Messaging for the project, select ENABLE.
Select Create credentials on the toolbar.
On the Add credentials to your project page, select API key link.
On API key page, select Create/Save. In the following example, the IP addresses option is selected, and 0.0.0.0/0 is entered for allowed IP addresses. You should restrict your API key appropriately.
Copy the API key to the clipboard, and save it somewhere.

You will use this API key value to enable Azure to authenticate with GCM and send push notifications on behalf of your app. To navigate back to the project dashboard, use the URL: https://console.developers.google.com/home/dashboard?project=

Create a notification hub

Sign in to the Azure portal.
Select Create a resource > Mobile > Notification Hub.
In the Notification Hub box, type a unique name. Select your Region, Subscription, and Resource Group (if you have one already).

If you don't already have a service bus namespace, you can use the default name, which is created based on the hub name (if the namespace name is available).

If you already have a service bus namespace that you want to create the hub in, follow these steps

a. In the Namespace area, select the Select Existing link.

b. Select Create.
Select Notifications (Bell icon), and select Go to resource.
Select Access Policies from the list. Note the two connection strings that are available to you. You need them to handle push notifications later.

Important
Do NOT use the DefaultFullSharedAccessSignature in your application. This is meant to be used in your back-end only.

Configure GCM setting for the notification hub

Select Google (GCM) in NOTIFICATON SETTINGS.
Enter API Key you got from the Google Cloud Console.
Select Save on the toolbar.

Your notification hub is now configured to work with GCM, and you have the connection strings to both register your app to receive and send push notifications.

Connect your app to the notification hub

Create a new Android project

In Android Studio, start a new Android Studio project.
Choose the Phone and Tablet form factor and the Minimum SDK that you want to support. Then click Next.
Choose Empty Activity for the main activity, click Next, and then click Finish.

Add Google Play services to the project

Open the Android SDK Manager by clicking the icon on the toolbar of Android Studio or by clicking Tools > Android > SDK Manager on the menu. Locate the target version of the Android SDK that is used in your project, open it by clicking Show Package Details, and choose Google APIs, if it is not already installed.
Click the SDK Tools tab. If you haven't already installed Google Play Service, click Google Play Services as shown below. Then click Apply to install.

Note the SDK path, for use in a later step.
Open the build.gradle file in the app directory.

Add this line under dependencies:

    compile 'com.google.android.gms:play-services-gcm:12.0.0'

Click the Sync Project with Gradle Files icon in the tool bar.

Open AndroidManifest.xml and add this tag to the application tag.

<meta-data android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version" />

Adding Azure Notification Hubs libraries

In the Build.Gradle file for the app, add the following lines in the dependencies section.

    compile 'com.microsoft.azure:notification-hubs-android-sdk:0.4@aar'
    compile 'com.microsoft.azure:azure-notifications-handler:1.0.1@aar'

Add the following repository after the dependencies section.

repositories {
    maven {
        url "http://dl.bintray.com/microsoftazuremobile/SDK"
    }
}

Updating the AndroidManifest.xml.

To support GCM, implement an Instance ID listener service in the code that is used to obtain registration tokens using Google's Instance ID API. In this tutorial, the name of the class is MyInstanceIDService.

Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with your actual package name shown at the top of the AndroidManifest.xml file.
```
<service android:name="<your package>.MyInstanceIDService" android:exported="false">
    <intent-filter>
        <action android:name="com.google.android.gms.iid.InstanceID"/>
    </intent-filter>
</service>
```
Once the application receives the GCM registration token from the Instance ID API, it uses the token to register with the Azure Notification Hub. The registration in the background is done using an IntentService named RegistrationIntentService. This service is responsible for refreshing the GCM registration token.

Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with your actual package name shown at the top of the AndroidManifest.xml file.
```
<service
    android:name="<your package>.RegistrationIntentService"
    android:exported="false">
</service>
```

Define a receiver to receive notifications. Add the following receiver definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with your actual package name shown at the top of the AndroidManifest.xml file.

<receiver android:name="com.microsoft.windowsazure.notifications.NotificationsBroadcastReceiver"
    android:permission="com.google.android.c2dm.permission.SEND">
    <intent-filter>
        <action android:name="com.google.android.c2dm.intent.RECEIVE" />
        <category android:name="<your package name>" />
    </intent-filter>
</receiver>

Add the following necessary GCM permissions below the </application> tag. Replace <your package> with the package name shown at the top of the AndroidManifest.xml file.

For more information on these permissions, see Setup a GCM Client app for Android.

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.GET_ACCOUNTS"/>
<uses-permission android:name="android.permission.WAKE_LOCK"/>
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

<permission android:name="<your package>.permission.C2D_MESSAGE" android:protectionLevel="signature" />
<uses-permission android:name="<your package>.permission.C2D_MESSAGE"/>

Adding code

In the Project View, expand app > src > main > java. Right-click your package folder under java, click New, and then click Java Class. Add a new class named NotificationSettings.

Update the three placeholders in the following code for the NotificationSettings class:
- SenderId: The project number you obtained earlier in the Google Cloud Console.
- HubListenConnectionString: The DefaultListenAccessSignature connection string for your hub. You can copy that connection string by clicking Access Policies on the Settings page of your hub on the Azure portal.
- HubName: Use the name of your notification hub that appears in the hub page in the Azure portal.
  
  NotificationSettings code:
```
public class NotificationSettings {

   public static String SenderId = "<Your project number>";
   public static String HubName = "<Your HubName>";
   public static String HubListenConnectionString = "<Your default listen connection string>";
}
```

Add another new class named MyInstanceIDService. This class is the Instance ID listener service implementation.

The code for this class calls IntentService to refresh the GCM token in the background.

import android.content.Intent;
import android.util.Log;
import com.google.android.gms.iid.InstanceIDListenerService;

public class MyInstanceIDService extends InstanceIDListenerService {

    private static final String TAG = "MyInstanceIDService";

    @Override
    public void onTokenRefresh() {

        Log.i(TAG, "Refreshing GCM Registration Token");

        Intent intent = new Intent(this, RegistrationIntentService.class);
        startService(intent);
    }
};

Add another new class to your project named, RegistrationIntentService. This class implements IntentService that handles refreshing the GCM token and registering with the notification hub.

Use the following code for this class.

import android.app.IntentService;
import android.content.Intent;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;
import android.util.Log;

import com.google.android.gms.gcm.GoogleCloudMessaging;
import com.google.android.gms.iid.InstanceID;
import com.microsoft.windowsazure.messaging.NotificationHub;

public class RegistrationIntentService extends IntentService {

    private static final String TAG = "RegIntentService";

    private NotificationHub hub;

    public RegistrationIntentService() {
        super(TAG);
    }

    @Override
    protected void onHandleIntent(Intent intent) {        
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        String resultString = null;
        String regID = null;

        try {
            InstanceID instanceID = InstanceID.getInstance(this);
            String token = instanceID.getToken(NotificationSettings.SenderId,
                    GoogleCloudMessaging.INSTANCE_ID_SCOPE);        
            Log.i(TAG, "Got GCM Registration Token: " + token);

            // Storing the registration id that indicates whether the generated token has been
            // sent to your server. If it is not stored, send the token to your server,
            // otherwise your server should have already received the token.
            if ((regID=sharedPreferences.getString("registrationID", null)) == null) {        
                NotificationHub hub = new NotificationHub(NotificationSettings.HubName,
                        NotificationSettings.HubListenConnectionString, this);
                Log.i(TAG, "Attempting to register with NH using token : " + token);

                regID = hub.register(token).getRegistrationId();

                // If you want to use tags...
                // Refer to : https://azure.microsoft.com/documentation/articles/notification-hubs-routing-tag-expressions/
                // regID = hub.register(token, "tag1", "tag2").getRegistrationId();

                resultString = "Registered Successfully - RegId : " + regID;
                Log.i(TAG, resultString);        
                sharedPreferences.edit().putString("registrationID", regID ).apply();
            } else {
                resultString = "Previously Registered Successfully - RegId : " + regID;
            }
        } catch (Exception e) {
            Log.e(TAG, resultString="Failed to complete token refresh", e);
            // If an exception happens while fetching the new token or updating the registration data
            // on a third-party server, this ensures that we'll attempt the update at a later time.
        }

        // Notify UI that registration has completed.
        if (MainActivity.isVisible) {
            MainActivity.mainActivity.ToastNotify(resultString);
        }
    }
}

In your MainActivity class, add the following import statements at the beginning of the class.

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GoogleApiAvailability;
import com.google.android.gms.gcm.*;
import com.microsoft.windowsazure.notifications.NotificationsManager;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;
import android.content.Intent;

Add the following private members at the top of the class. This code checks the availability of Google Play Services as recommended by Google.

public static MainActivity mainActivity;
public static Boolean isVisible = false;    
private GoogleCloudMessaging gcm;
private static final int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
private static final String TAG = "MainActivity";

In your MainActivity class, add the following method to the availability of Google Play Services.

/**
    * Check the device to make sure it has the Google Play Services APK. If
    * it doesn't, display a dialog that allows users to download the APK from
    * the Google Play Store or enable it in the device's system settings.
    */
private boolean checkPlayServices() {
    GoogleApiAvailability apiAvailability = GoogleApiAvailability.getInstance();
    int resultCode = apiAvailability.isGooglePlayServicesAvailable(this);
    if (resultCode != ConnectionResult.SUCCESS) {
        if (apiAvailability.isUserResolvableError(resultCode)) {
            apiAvailability.getErrorDialog(this, resultCode, PLAY_SERVICES_RESOLUTION_REQUEST)
                    .show();
        } else {
            Log.i(TAG, "This device is not supported by Google Play Services.");
            ToastNotify("This device is not supported by Google Play Services.");
            finish();
        }
        return false;
    }
    return true;
}

In your MainActivity class, add the following code that checks for Google Play Services before calling your IntentService to get your GCM registration token and register with your notification hub.

public void registerWithNotificationHubs()
{
    Log.i(TAG, " Registering with Notification Hubs");

    if (checkPlayServices()) {
        // Start IntentService to register this application with GCM.
        Intent intent = new Intent(this, RegistrationIntentService.class);
        startService(intent);
    }
}

In the OnCreate method of the MainActivity class, add the following code to start the registration process when activity is created.

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

    mainActivity = this;
    NotificationsManager.handleNotifications(this, NotificationSettings.SenderId, MyHandler.class);
    registerWithNotificationHubs();
}

Add these additional methods to the MainActivity to verify app state and report status in your app.

@Override
protected void onStart() {
    super.onStart();
    isVisible = true;
}

@Override
protected void onPause() {
    super.onPause();
    isVisible = false;
}

@Override
protected void onResume() {
    super.onResume();
    isVisible = true;
}

@Override
protected void onStop() {
    super.onStop();
    isVisible = false;
}

public void ToastNotify(final String notificationMessage) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            Toast.makeText(MainActivity.this, notificationMessage, Toast.LENGTH_LONG).show();
            TextView helloText = (TextView) findViewById(R.id.text_hello);
            helloText.setText(notificationMessage);
        }
    });
}

The ToastNotify method uses the "Hello World" TextView control to report status and notifications persistently in the app. In your activity_main.xml layout, add the following ID for that control.
```
android:id="@+id/text_hello"
```
Add a subclass for the receiver that's defined in the AndroidManifest.xml. Add another new class to your project named MyHandler.

Add the following import statements at the top of MyHandler.java:

import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import com.microsoft.windowsazure.notifications.NotificationsHandler;
import android.net.Uri;
import android.media.RingtoneManager;

Add the following code for the MyHandler class making it a subclass of com.microsoft.windowsazure.notifications.NotificationsHandler.

This code overrides the OnReceive method, so the handler reports notifications that are received. The handler also sends the push notification to the Android notification manager by using the sendNotification() method. The sendNotification() method should be executed when the app is not running and a notification is received.

public class MyHandler extends NotificationsHandler {
    public static final int NOTIFICATION_ID = 1;
    private NotificationManager mNotificationManager;
    NotificationCompat.Builder builder;
    Context ctx;

    @Override
    public void onReceive(Context context, Bundle bundle) {
        ctx = context;
        String nhMessage = bundle.getString("message");
        sendNotification(nhMessage);
        if (MainActivity.isVisible) {
            MainActivity.mainActivity.ToastNotify(nhMessage);
        }
    }

    private void sendNotification(String msg) {

        Intent intent = new Intent(ctx, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        mNotificationManager = (NotificationManager)
                ctx.getSystemService(Context.NOTIFICATION_SERVICE);

        PendingIntent contentIntent = PendingIntent.getActivity(ctx, 0,
                intent, PendingIntent.FLAG_ONE_SHOT);

        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder mBuilder =
                new NotificationCompat.Builder(ctx)
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setContentTitle("Notification Hub Demo")
                        .setStyle(new NotificationCompat.BigTextStyle()
                                .bigText(msg))
                        .setSound(defaultSoundUri)
                        .setContentText(msg);

        mBuilder.setContentIntent(contentIntent);
        mNotificationManager.notify(NOTIFICATION_ID, mBuilder.build());
    }
}

In Android Studio on the menu bar, click Build > Rebuild Project to make sure that no errors are present in your code.

Testing your app

Run the mobile application

Run the app and notice that the registration ID is reported for a successful registration.
Enter a notification message to be sent to all Android devices that have registered with the hub.
Press Send Notification. Any devices that have the app running shows an AlertDialog instance with the push notification message. Devices that don't have the app running but were previously registered for push notifications receive a notification in the Android Notification Manager. The notification messages can be viewed by swiping down from the upper-left corner.

Test send push notifications from the Azure portal

You can test receiving push notifications in your app by sending them via the Azure portal.

In the Troubleshooting section, select Test Send.
For Platforms, select Android.
Select Send to send the test notification.
Confirm that you see the notification message on the Android device.

Push notifications are normally sent in a back-end service like Mobile Apps or ASP.NET using a compatible library. If a library is not available for your back-end you can also use the REST API directly to send notification messages.

Here is a list of some other tutorials you may want to review for sending notifications:

Azure Mobile Apps: For an example of how to send notifications from a Mobile Apps back-end integrated with Notification Hubs, see Add Push Notifications to your iOS App.
ASP.NET: Use Notification Hubs to push notifications to users.
Azure Notification Hub Java SDK: See How to use Notification Hubs from Java for sending notifications from Java. This has been tested in Eclipse for Android Development.
PHP: How to use Notification Hubs from PHP.

Push notifications in the emulator

If you want to test push notifications inside an emulator, make sure that your emulator image supports the Google API level that you chose for your app. If your image doesn't support native Google APIs, you end up with the SERVICE_NOT_AVAILABLE exception.

In addition, ensure that you have added your Google account to your running emulator under Settings > Accounts. Otherwise, your attempts to register with GCM may result in the AUTHENTICATION_FAILED exception.

(Optional) Send push notifications directly from the app

Normally, you would send notifications using a backend server. For some cases, you might want to be able to send push notifications directly from the client application. This section explains how to send notifications from the client using the Azure Notification Hub REST API.

In Android Studio Project View, expand App > src > main > res > layout. Open the activity_main.xml layout file and click the Text tab to update the text contents of the file. Update it with the code below, which adds new Button and EditText controls for sending push notification messages to the notification hub. Add this code at the bottom, just before </RelativeLayout>.

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/send_button"
android:id="@+id/sendbutton"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:onClick="sendNotificationButtonOnClick" />

<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/editTextNotificationMessage"
android:layout_above="@+id/sendbutton"
android:layout_centerHorizontal="true"
android:layout_marginBottom="42dp"
android:hint="@string/notification_message_hint" />

In Android Studio Project View, expand App > src > main > res > values. Open the strings.xml file and add the string values that are referenced by the new Button and EditText controls. Add the following lines at the bottom of the file, just before </resources>.
```
<string name="send_button">Send Notification</string>
<string name="notification_message_hint">Enter notification message text</string>
```
In your NotificationSetting.java file, add the following setting to the NotificationSettings class.

Update HubFullAccess with the DefaultFullSharedAccessSignature connection string for your hub. This connection string can be copied from the Azure portal by clicking Access Policies on the Settings page for your notification hub.
```
public static String HubFullAccess = "<Enter Your DefaultFullSharedAccess Connection string>";
```

In your MainActivity.java file, add the following import statements at the beginning of the file.

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import android.util.Base64;
import android.view.View;
import android.widget.EditText;

In your MainActivity.java file, add the following members at the top of the MainActivity class.

private String HubEndpoint = null;
private String HubSasKeyName = null;
private String HubSasKeyValue = null;

Create a Software Access Signature (SaS) token to authenticate a POST request to send messages to your notification hub. Parse the key data from the connection string and then creating the SaS token, as mentioned in the Common Concepts REST API reference. The following code is an example implementation.

In MainActivity.java, add the following method to the MainActivity class to parse your connection string.

/**
    * Example code from http://msdn.microsoft.com/library/azure/dn495627.aspx
    * to parse the connection string so a SaS authentication token can be
    * constructed.
    *
    * @param connectionString This must be the DefaultFullSharedAccess connection
    *                         string for this example.
    */
private void ParseConnectionString(String connectionString)
{
    String[] parts = connectionString.split(";");
    if (parts.length != 3)
        throw new RuntimeException("Error parsing connection string: "
                + connectionString);

    for (int i = 0; i < parts.length; i++) {
        if (parts[i].startsWith("Endpoint")) {
            this.HubEndpoint = "https" + parts[i].substring(11);
        } else if (parts[i].startsWith("SharedAccessKeyName")) {
            this.HubSasKeyName = parts[i].substring(20);
        } else if (parts[i].startsWith("SharedAccessKey")) {
            this.HubSasKeyValue = parts[i].substring(16);
        }
    }
}

In MainActivity.java, add the following method to the MainActivity class to create a SaS authentication token.

/**
    * Example code from http://msdn.microsoft.com/library/azure/dn495627.aspx to
    * construct a SaS token from the access key to authenticate a request.
    *
    * @param uri The unencoded resource URI string for this operation. The resource
    *            URI is the full URI of the Service Bus resource to which access is
    *            claimed. For example,
    *            "http://<namespace>.servicebus.windows.net/<hubName>"
    */
private String generateSasToken(String uri) {

    String targetUri;
    String token = null;
    try {
        targetUri = URLEncoder
                .encode(uri.toString().toLowerCase(), "UTF-8")
                .toLowerCase();

        long expiresOnDate = System.currentTimeMillis();
        int expiresInMins = 60; // 1 hour
        expiresOnDate += expiresInMins * 60 * 1000;
        long expires = expiresOnDate / 1000;
        String toSign = targetUri + "\n" + expires;

        // Get an hmac_sha1 key from the raw key bytes
        byte[] keyBytes = HubSasKeyValue.getBytes("UTF-8");
        SecretKeySpec signingKey = new SecretKeySpec(keyBytes, "HmacSHA256");

        // Get an hmac_sha1 Mac instance and initialize with the signing key
        Mac mac = Mac.getInstance("HmacSHA256");
        mac.init(signingKey);

        // Compute the hmac on input data bytes
        byte[] rawHmac = mac.doFinal(toSign.getBytes("UTF-8"));

        // Using android.util.Base64 for Android Studio instead of
        // Apache commons codec
        String signature = URLEncoder.encode(
                Base64.encodeToString(rawHmac, Base64.NO_WRAP).toString(), "UTF-8");

        // Construct authorization string
        token = "SharedAccessSignature sr=" + targetUri + "&sig="
                + signature + "&se=" + expires + "&skn=" + HubSasKeyName;
    } catch (Exception e) {
        if (isVisible) {
            ToastNotify("Exception Generating SaS : " + e.getMessage().toString());
        }
    }

    return token;
}

In MainActivity.java, add the following method to the MainActivity class to handle the Send Notification button click and send the push notification message to the hub by using the built-in REST API.

/**
    * Send Notification button click handler. This method parses the
    * DefaultFullSharedAccess connection string and generates a SaS token. The
    * token is added to the Authorization header on the POST request to the
    * notification hub. The text in the editTextNotificationMessage control
    * is added as the JSON body for the request to add a GCM message to the hub.
    *
    * @param v
    */
public void sendNotificationButtonOnClick(View v) {
    EditText notificationText = (EditText) findViewById(R.id.editTextNotificationMessage);
    final String json = "{\"data\":{\"message\":\"" + notificationText.getText().toString() + "\"}}";

    new Thread()
    {
        public void run()
        {
            try
            {
                // Based on reference documentation...
                // http://msdn.microsoft.com/library/azure/dn223273.aspx
                ParseConnectionString(NotificationSettings.HubFullAccess);
                URL url = new URL(HubEndpoint + NotificationSettings.HubName +
                        "/messages/?api-version=2015-01");

                HttpURLConnection urlConnection = (HttpURLConnection)url.openConnection();

                try {
                    // POST request
                    urlConnection.setDoOutput(true);

                    // Authenticate the POST request with the SaS token
                    urlConnection.setRequestProperty("Authorization", 
                        generateSasToken(url.toString()));

                    // Notification format should be GCM
                    urlConnection.setRequestProperty("ServiceBusNotification-Format", "gcm");

                    // Include any tags
                    // Example below targets 3 specific tags
                    // Refer to : https://azure.microsoft.com/documentation/articles/notification-hubs-routing-tag-expressions/
                    // urlConnection.setRequestProperty("ServiceBusNotification-Tags", 
                    //        "tag1 || tag2 || tag3");

                    // Send notification message
                    urlConnection.setFixedLengthStreamingMode(json.length());
                    OutputStream bodyStream = new BufferedOutputStream(urlConnection.getOutputStream());
                    bodyStream.write(json.getBytes());
                    bodyStream.close();

                    // Get reponse
                    urlConnection.connect();
                    int responseCode = urlConnection.getResponseCode();
                    if ((responseCode != 200) && (responseCode != 201)) {
                        BufferedReader br = new BufferedReader(new InputStreamReader((urlConnection.getErrorStream())));
                        String line;
                        StringBuilder builder = new StringBuilder("Send Notification returned " +
                                responseCode + " : ")  ;
                        while ((line = br.readLine()) != null) {
                            builder.append(line);
                        }

                        ToastNotify(builder.toString());
                    }
                } finally {
                    urlConnection.disconnect();
                }
            }
            catch(Exception e)
            {
                if (isVisible) {
                    ToastNotify("Exception Sending Notification : " + e.getMessage().toString());
                }
            }
        }
    }.start();
}

Next steps

In this tutorial, you sent broadcast notifications to all your Android devices registered with the backend. To learn how to push notifications to specific Android devices, advance to the following tutorial:

Push notifications to specific devices