Firebase cloud messaging to send push Notifications

In this blog, I will show you how you can send the Push notification to your users on their mobile phone using the Firebase cloud messaging. As in any mobile application like WhatsApp, hike, Paytm and phonePe etc. push notification plays a very important role to inform the user about the new notification. why we need push notifications?
Like in Facebook Messenger when you are using facebook messenger and you are chatting with someone you get to know when someone sends you a message and you can easily chat with them, but what happens if your phone is idle and you are not using that, and someone sends you a message if push notifications are not enabled then you will not get to know about that message instantly, you have to open the messenger then you get to know that you have received a message. But if Push notifications are enabled you get a notification with the notification sound that you have received a message from the sender name.so you can understand the importance of the push notifications.
I Will show you how you can interact with firebase using java application to send a notification to users. To implement Firebase in java you need two things Firebase API URL and Firebase-Server Key.you can find the firebase API URL on the official site of firebase cloud messaging and for firebase server Key The Mobile App developer will provide you that key. Now the big point is How to send messages to the user.
here is the code in spring-boot:

public class FirebaseService {
	private static Logger logger = LoggerFactory.getLogger(FirebaseService.class);
	@Autowired
	private FirebaseRepository firebaseRepository;

	@Value("${firebase.api.url}")
	private String firebaseApiUrl;

	@Value("${firebase.server.key}")
	private String firebaseServerKey;

	@KafkaListener(topicPartitions = @TopicPartition(topic = DataConstants.KAFKA_NOTIFICATION_TOPIC, partitions = {
			"0" }))
	public void sendPushNotification(ConsumerRecord consumerRecord) throws IOException {
		FirebaseDTO firebaseDTO = ObjectSerializer.getObject(consumerRecord.value(), FirebaseDTO.class);
		if (firebaseDTO.getDeviceToken() == null || firebaseDTO.getDeviceType() == null
				|| firebaseDTO.getMessage() == null || firebaseDTO.getNotificationType() == null
				|| firebaseDTO.getUserId() == null) {
			logger.info("required data is missing");
		} else {
			URL url = new URL(firebaseApiUrl);
			HttpURLConnection conn = makeHttpConnection(url);
			JSONObject json = new JSONObject();
			Map userUpdates = new HashMap<>();
			userUpdates.put(DataConstants.TITTLE, firebaseDTO.getNotificationType());
			try {
				setDataInJson(json, userUpdates, firebaseDTO);
			} catch (Exception ex) {
				logger.error(ex.getMessage());
				ex.printStackTrace();
			}
			String firebaseMessage = "";
			try {
				logger.info("json data is : {}", json);
				// firebaseMessage = sendMessageToFirebase(conn, json);
			} catch (Exception ex) {
				logger.error(ex.getMessage());
				ex.printStackTrace();
			}
			if (firebaseMessage.contains("message_id")) {
				logger.info("GCM Notification is sent successfully");
			} else {
				logger.info("GCM Notification sending failed");
			}
			Firebase firebase = new Firebase();
			firebase.setRead(false);
			firebase.setUserId(firebaseDTO.getUserId());
			firebase.setMessage(firebaseDTO.getMessage());
			firebase.setNotificationType(firebaseDTO.getNotificationType());
			firebase.setDeliveryStatus("success");
			firebase.setDeviceType(firebaseDTO.getDeviceType());
			Date date = new Date();
			firebase.setMessageDate(date);
			firebaseRepository.save(firebase);
		}
	}

	/**
	 * krishna 05-Sep-2018
	 */
	public String sendMessageToFirebase(HttpURLConnection conn, JSONObject json) {
		String message = "";
		try {
			OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
			wr.write(json.toString());
			wr.flush();
			BufferedReader br = new BufferedReader(new InputStreamReader((conn.getInputStream())));
			logger.info("buffer reader is :{}", br);
			String output;
			while ((output = br.readLine()) != null) {
				logger.info("notification : {}", output);
				message = output;
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return message;
	}

	/**
	 * krishna 05-Sep-2018
	 */
	public void setDataInJson(JSONObject json, Map userUpdates, FirebaseDTO firebaseDTO) {
		try {
			logger.info("device-type: {}", firebaseDTO.getDeviceType());
			logger.info("device-token: {}", firebaseDTO.getDeviceToken());
			json.put("to", firebaseDTO.getDeviceToken().trim());
			if (firebaseDTO.getDeviceType().equals(DeviceType.IOS)) {
				logger.info("IOS:-");
				userUpdates.put("body", firebaseDTO.getMessage());
				json.put("notification", userUpdates);
				json.put("priority", "high");
			} else if (firebaseDTO.getDeviceType().equals(DeviceType.ANDROID)) {
				logger.info("android:-");
				userUpdates.put("message", firebaseDTO.getMessage());
				json.put("data", userUpdates);
			} else {
				logger.info("not android and ios:-");
				userUpdates.put("message", firebaseDTO.getMessage());
				json.put("data", userUpdates);
			}
		} catch (JSONException e1) {
			e1.printStackTrace();
		}
	}

	/**
	 * krishna 05-Sep-2018
	 */
	public HttpURLConnection makeHttpConnection(URL url) {
		HttpURLConnection conn = null;
		try {
			conn = (HttpURLConnection) url.openConnection();
			conn.setUseCaches(false);
			conn.setDoInput(true);
			conn.setDoOutput(true);
			conn.setRequestMethod("POST");
			conn.setRequestProperty("Authorization", "key=" + firebaseServerKey);
			conn.setRequestProperty("Content-Type", "application/json");
		} catch (Exception ex) {
			logger.error(ex.getMessage());
			ex.printStackTrace();
		}
		return conn;
	}
}                

#####Firebase DTO #######

public class FirebaseDTO {
	@NotNull
	private String deviceToken;
	@NotNull
	private String message;
	@NotNull
	private DeviceType deviceType;
	@NotNull
	private NotificationType notificationType;
	@NotNull
	private Long userId;

	/**
	 * @return the deviceToken
	 */
	public String getDeviceToken() {
		return deviceToken;
	}

	/**
	 * @param deviceToken
	 *            the deviceToken to set
	 */
	public void setDeviceToken(String deviceToken) {
		this.deviceToken = deviceToken;
	}

	/**
	 * @return the message
	 */
	public String getMessage() {
		return message;
	}

	/**
	 * @param message
	 *            the message to set
	 */
	public void setMessage(String message) {
		this.message = message;
	}

	/**
	 * @return the deviceType
	 */
	public DeviceType getDeviceType() {
		return deviceType;
	}

	/**
	 * @param deviceType
	 *            the deviceType to set
	 */
	public void setDeviceType(DeviceType deviceType) {
		this.deviceType = deviceType;
	}

	/**
	 * @return the notificationType
	 */
	public NotificationType getNotificationType() {
		return notificationType;
	}

	/**
	 * @param notificationType
	 *            the notificationType to set
	 */
	public void setNotificationType(NotificationType notificationType) {
		this.notificationType = notificationType;
	}

	/**
	 * @return the userId
	 */
	public Long getUserId() {
		return userId;
	}

	/**
	 * @param userId the userId to set
	 */
	public void setUserId(Long userId) {
		this.userId = userId;
	}
}
 

here Device Token is the unique Mobile Token which is provided to you by the mobile application Developer.
Thanks