Send push notification on button click
<p>I want to send push notification from one device to multiple device using GCM in the button click. I have followed the all process of GCM. I got the server key and registration ID of the device but I didn't get the push notification using GCM. I have also searched on the google but didn't get the right solution for that.  </p>

<p>Please suggest me how to send push notification on the multiple device.  </p>

<p><code>MainActivity.java</code>  </p>

<pre><code>public class MainActivity extends AppCompatActivity {
    private static final int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
    private static final String TAG = "MainActivity";

    private BroadcastReceiver mRegistrationBroadcastReceiver;
    private ProgressBar mRegistrationProgressBar;
    private TextView mInformationTextView;
    private boolean isReceiverRegistered;

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

        mRegistrationProgressBar = (ProgressBar) findViewById(R.id.registrationProgressBar);
        mRegistrationBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                mRegistrationProgressBar.setVisibility(ProgressBar.GONE);
                SharedPreferences sharedPreferences =
                        PreferenceManager.getDefaultSharedPreferences(context);
                boolean sentToken = sharedPreferences
                        .getBoolean(QuickstartPreferences.SENT_TOKEN_TO_SERVER, false);
                if (sentToken) {
                    mInformationTextView.setText(getString(R.string.gcm_send_message));
                } else {
                    mInformationTextView.setText(getString(R.string.token_error_message));
                }
            }
        };
        mInformationTextView = (TextView) findViewById(R.id.informationTextView);

        // Registering BroadcastReceiver
        registerReceiver();

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

    @Override
    protected void onResume() {
        super.onResume();
        registerReceiver();
    }

    @Override
    protected void onPause() {
        LocalBroadcastManager.getInstance(this).unregisterReceiver(mRegistrationBroadcastReceiver);
        isReceiverRegistered = false;
        super.onPause();
    }

    private void registerReceiver(){
        if(!isReceiverRegistered) {
            LocalBroadcastManager.getInstance(this).registerReceiver(mRegistrationBroadcastReceiver,
                    new IntentFilter(QuickstartPreferences.REGISTRATION_COMPLETE));
            isReceiverRegistered = true;
        }
    }
    /**
     * 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.");
                finish();
            }
            return false;
        }
        return true;
    }

}  
</code></pre>

<p><code>MyGcmListenerService.java</code>  </p>

<pre><code>public class MyGcmListenerService extends GcmListenerService {
    private static final String TAG = "MyGcmListenerService";
    public static final int NOTIFICATION_ID = 1;
    private NotificationManager mNotificationManager;
    NotificationCompat.Builder builder;


    /**
     * Called when message is received.
     *
     * @param from SenderID of the sender.
     * @param data Data bundle containing message data as key/value pairs.
     *             For Set of keys use data.keySet().
     */
    // [START receive_message]
    @Override
    public void onMessageReceived(String from, Bundle data) {
        String message = data.getString("message");
        Log.d(TAG, "From: " + from);
        Log.d(TAG, "Message: " + message);

        if (from.startsWith("/topics/")) {
            // message received from some topic.
        } else {
            // normal downstream message.
        }

        // [START_EXCLUDE]
        /**
         * Production applications would usually process the message here.
         * Eg: - Syncing with server.
         *     - Store message in local database.
         *     - Update UI.
         */

        /**
         * In some cases it may be useful to show a notification indicating to the user
         * that a message was received.
         */
        sendNotification(message);
        // [END_EXCLUDE]
    }
    // [END receive_message]

    /**
     * Create and show a simple notification containing the received GCM message.
     *
     * @param message GCM message received.
     */
    private void sendNotification(String message) {
        Log.d(TAG, "Preparing to send notification...: " + message);
        mNotificationManager = (NotificationManager) this
                .getSystemService(Context.NOTIFICATION_SERVICE);

        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
                new Intent(this, MainActivity.class), 0);

        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(
                this).setSmallIcon(R.drawable.ic_launcher)
                .setContentTitle("GCM Notification")
                .setSound(defaultSoundUri)
                .setStyle(new NotificationCompat.BigTextStyle().bigText(message))
                .setContentText(message);

        mBuilder.setContentIntent(contentIntent);
        mNotificationManager.notify(NOTIFICATION_ID, mBuilder.build());
        Log.d(TAG, "Notification sent successfully.");
    }
}  
</code></pre>

<p><code>RegistrationIntentService.java</code>  </p>

<pre><code>public class RegistrationIntentService extends IntentService {

    private static final String TAG = "RegIntentService";
    private static final String[] TOPICS = {"global"};

    public RegistrationIntentService() {
        super(TAG);
    }

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

        try {
            // [START register_for_gcm]
            // Initially this call goes out to the network to retrieve the token, subsequent calls
            // are local.
            // R.string.gcm_defaultSenderId (the Sender ID) is typically derived from google-services.json.
            // See https://developers.google.com/cloud-messaging/android/start for details on this file.
            // [START get_token]
            InstanceID instanceID = InstanceID.getInstance(this);
            String token = instanceID.getToken(getString(R.string.gcm_defaultSenderIdd),
                    GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
            // [END get_token]
            Log.i(TAG, "GCM Registration Token: " + token);

            // TODO: Implement this method to send any registration to your app's servers.
            sendRegistrationToServer(token);

            // Subscribe to topic channels
            subscribeTopics(token);

            // You should store a boolean that indicates whether the generated token has been
            // sent to your server. If the boolean is false, send the token to your server,
            // otherwise your server should have already received the token.
            sharedPreferences.edit().putBoolean(QuickstartPreferences.SENT_TOKEN_TO_SERVER, true).apply();
            // [END register_for_gcm]
        } catch (Exception e) {
            Log.d(TAG, "Failed to complete token refresh", e);
            // If an exception happens while fetching the new token or updating our registration data
            // on a third-party server, this ensures that we'll attempt the update at a later time.
            sharedPreferences.edit().putBoolean(QuickstartPreferences.SENT_TOKEN_TO_SERVER, false).apply();
        }
        // Notify UI that registration has completed, so the progress indicator can be hidden.
        Intent registrationComplete = new Intent(QuickstartPreferences.REGISTRATION_COMPLETE);
        LocalBroadcastManager.getInstance(this).sendBroadcast(registrationComplete);
    }

    /**
     * Persist registration to third-party servers.
     *
     * Modify this method to associate the user's GCM registration token with any server-side account
     * maintained by your application.
     *
     * @param token The new token.
     */
    private void sendRegistrationToServer(String token) {
        // Add custom implementation, as needed.
    }

    /**
     * Subscribe to any GCM topics of interest, as defined by the TOPICS constant.
     *
     * @param token GCM token
     * @throws IOException if unable to reach the GCM PubSub service
     */
    // [START subscribe_topics]
    private void subscribeTopics(String token) throws IOException {
        GcmPubSub pubSub = GcmPubSub.getInstance(this);
        for (String topic : TOPICS) {
            pubSub.subscribe(token, "/topics/" + topic, null);
        }
    }
    // [END subscribe_topics]
}  
</code></pre>

<p><code>GcmSender.java</code>  </p>

<pre><code>public class GcmSender {
    public static final String API_KEY = "AIzaSyClNEQb0X2Pp8k6_JaZx_XWnJAzsm3VSDQ";

    public static void main(String[] args) throws JSONException {
        if (args.length &lt; 1 || args.length &gt; 2 || args[0] == null) {
            System.err.println("usage: ./gradlew run -Pmsg=\"MESSAGE\" [-Pto=\"DEVICE_TOKEN\"]");
            System.err.println("");
            System.err.println("Specify a test message to broadcast via GCM. If a device's GCM registration token is\n" +
                    "specified, the message will only be sent to that device. Otherwise, the message \n" +
                    "will be sent to all devices subscribed to the \"global\" topic.");
            System.err.println("");
            System.err.println("Example (Broadcast):\n" +
                    "On Windows:   .\\gradlew.bat run -Pmsg=\"&lt;Your_Message&gt;\"\n" +
                    "On Linux/Mac: ./gradlew run -Pmsg=\"&lt;Your_Message&gt;\"");
            System.err.println("");
            System.err.println("Example (Unicast):\n" +
                    "On Windows:   .\\gradlew.bat run -Pmsg=\"&lt;Your_Message&gt;\" -Pto=\"&lt;Your_Token&gt;\"\n" +
                    "On Linux/Mac: ./gradlew run -Pmsg=\"&lt;Your_Message&gt;\" -Pto=\"&lt;Your_Token&gt;\"");
            System.exit(1);
        }
        try {
            // Prepare JSON containing the GCM message content. What to send and where to send.
            JSONObject jGcmData = new JSONObject();
            JSONObject jData = new JSONObject();
            jData.put("message", args[0].trim());
            // Where to send GCM message.
            if (args.length &gt; 1 &amp;&amp; args[1] != null) {
                jGcmData.put("to", args[1].trim());
            } else {
                jGcmData.put("to", "/topics/global");
            }
            // What to send in GCM message.
            jGcmData.put("data", jData);

            // Create connection to send GCM Message request.
            URL url = new URL("https://android.googleapis.com/gcm/send");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestProperty("Authorization", "key=" + API_KEY);
            conn.setRequestProperty("Content-Type", "application/json");
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);

            // Send GCM message content.
            OutputStream outputStream = conn.getOutputStream();
            outputStream.write(jGcmData.toString().getBytes());

            // Read GCM response.
            InputStream inputStream = conn.getInputStream();
            String resp = IOUtils.toString(inputStream);
            System.out.println(resp);
            System.out.println("Check your device/emulator for notification or logcat for " +
                    "confirmation of the receipt of the GCM message.");
        } catch (IOException e) {
            System.out.println("Unable to send GCM message.");
            System.out.println("Please ensure that API_KEY has been replaced by the server " +
                    "API key, and that the device's registration token is correct (if specified).");
            e.printStackTrace();
        }
    }

}
</code></pre>