FirebaseApp with name [DEFAULT] doesn't exist. (For Spring Boot)

I followed this link to create a fire base application-https://blog.mestwin.net/send-push-notifications-from-spring-boot-server-side-application-using-fcm/
And I am getting this error-FirebaseApp with name [DEFAULT] doesn't exist. (For Spring Boot)
I have added the JSON Key and and its path in application properties....Am not able to figure out where I Am going wrong...
This is my FCMInitializer-

import com.google.auth.oauth2.GoogleCredentials;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.ClassPathResource;
import org.springframework.stereotype.Service;

import javax.annotation.PostConstruct;
import java.io.IOException;



@Service
public class FCMInitializer {



    @Value("${app.firebase-configuration-file}")
    private String firebaseConfigPath;

    Logger logger = LoggerFactory.getLogger(FCMInitializer.class);

    @PostConstruct
    public void initialize() {
        try {
            FirebaseOptions options = new FirebaseOptions.Builder()
                    .setCredentials(GoogleCredentials.fromStream(new ClassPathResource(firebaseConfigPath).getInputStream())).build();
            if (FirebaseApp.getApps().isEmpty()) {
                FirebaseApp.initializeApp(options);
                logger.info("Firebase application has been initialized");
            }
        } catch (IOException e) {
            logger.error(e.getMessage());
        }
    }

}

This is my FCM Service-

import com.google.firebase.messaging.*;
import lombok.extern.slf4j.Slf4j;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;

import java.time.Duration;
import java.util.Map;
import java.util.concurrent.ExecutionException;

//import org.slf4j.LoggerFactory;
//import com.highpeak.av.pushnotification.dto.PushNotificationRequest;

@Slf4j
@Service
public class FCMService {

    private Logger logger = LoggerFactory.getLogger(FCMService.class);

    public void sendMessage(Map<String, String> data, PushNotificationRequest request)
            throws InterruptedException, ExecutionException {
        Message message = getPreconfiguredMessageWithData(data, request);
        String response = sendAndGetResponse(message);
        log.info("Sent message with data. Topic: " + request.getTopic() + ", " + response);
    }

    private Message getPreconfiguredMessageWithData(Map<String, String> data, PushNotificationRequest request) {
        return getPreconfiguredMessageBuilder(request).putAllData(data).setTopic(request.getTopic())
                .build();
    }



    public void sendMessageWithoutData(PushNotificationRequest request)
            throws InterruptedException, ExecutionException {
        Message message = getPreconfiguredMessageWithoutData(request);
        String response = sendAndGetResponse(message);
        log.info("Sent message without data. Topic: " + request.getTopic() + ", " + response);
    }



    private String sendAndGetResponse(Message message) throws InterruptedException, ExecutionException {
        return FirebaseMessaging.getInstance().sendAsync(message).get();
    }

    private AndroidConfig getAndroidConfig(String topic) {
        return AndroidConfig.builder()
                .setTtl(Duration.ofMinutes(2).toMillis()).setCollapseKey(topic)
                .setPriority(AndroidConfig.Priority.HIGH)
                .setNotification(AndroidNotification.builder().setSound(NotificationParameter.SOUND.getValue())
                        .setColor(NotificationParameter.COLOR.getValue()).setTag(topic).build()).build();
    }

    private ApnsConfig getApnsConfig(String topic) {
        return ApnsConfig.builder()
                .setAps(Aps.builder().setCategory(topic).setThreadId(topic).build()).build();
    }

    private Message getPreconfiguredMessageWithoutData(PushNotificationRequest request) {
        return getPreconfiguredMessageBuilder(request).setTopic(request.getTopic())
                .build();
    }



    private Message.Builder getPreconfiguredMessageBuilder(PushNotificationRequest request) {
        AndroidConfig androidConfig = getAndroidConfig(request.getTopic());
        ApnsConfig apnsConfig = getApnsConfig(request.getTopic());
        return Message.builder()
                .setApnsConfig(apnsConfig).setAndroidConfig(androidConfig).setNotification(
                        new Notification(request.getTitle(), request.getMessage()));
    }


    public void sendMessageToToken(PushNotificationRequest request)
            throws InterruptedException, ExecutionException {
        Message message = getPreconfiguredMessageToToken(request);
        String response = sendAndGetResponse(message);
        log.info("Sent message to token. Device token: " + request.getToken() + ", " + response);
    }


    private Message getPreconfiguredMessageToToken(PushNotificationRequest request) {
        return getPreconfiguredMessageBuilder(request).setToken(request.getToken())
                .build();
    }



}

This is my PushNotification Service-

package com.example.MyFirstPushNotificationService.PushNotificationsDemo;

import com.google.api.client.util.Value;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;

import java.time.LocalDateTime;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutionException;

@Service
public class PushNotificationService {

    @Value("#{${app.notifications.defaults}}")
    private Map<String, String> defaults;

    private Logger logger = LoggerFactory.getLogger(PushNotificationService.class);
    private FCMService fcmService;

    public PushNotificationService(FCMService fcmService) {
        this.fcmService = fcmService;
    }

    @Scheduled(initialDelay = 60000, fixedDelay = 60000)
    public void sendSamplePushNotification() {
        try {
            fcmService.sendMessageWithoutData(getSamplePushNotificationRequest());
        } catch (InterruptedException | ExecutionException e) {
            logger.error(e.getMessage());
        }
    }

    public void sendPushNotification(PushNotificationRequest request) {
        try {
            fcmService.sendMessage(getSamplePayloadData(), request);
        } catch (InterruptedException | ExecutionException e) {
            logger.error(e.getMessage());
        }
    }

    public void sendPushNotificationWithoutData(PushNotificationRequest request) {
        try {
            fcmService.sendMessageWithoutData(request);
        } catch (InterruptedException | ExecutionException e) {
            logger.error(e.getMessage());
        }
    }


    public void sendPushNotificationToToken(PushNotificationRequest request) {
        try {
            fcmService.sendMessageToToken(request);
        } catch (InterruptedException | ExecutionException e) {
            logger.error(e.getMessage());
        }
    }


    private Map<String, String> getSamplePayloadData() {
        Map<String, String> pushData = new HashMap<>();
        pushData.put("messageId", defaults.get("payloadMessageId"));
        pushData.put("text", defaults.get("payloadData") + " " + LocalDateTime.now());
        return pushData;
    }


    private PushNotificationRequest getSamplePushNotificationRequest() {
        PushNotificationRequest request = new PushNotificationRequest(defaults.get("title"),
                defaults.get("message"),
                defaults.get("topic"));
        return request;
    }


}

This is my PushNotificationController-

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class PushNotificationController {

    private PushNotificationService pushNotificationService;

    public PushNotificationController(PushNotificationService pushNotificationService) {
        this.pushNotificationService = pushNotificationService;
    }

    @PostMapping("/notification/topic")
    public ResponseEntity sendNotification(@RequestBody PushNotificationRequest request) {
        pushNotificationService.sendPushNotificationWithoutData(request);
        return new ResponseEntity<>(new PushNotificationResponse(HttpStatus.OK.value(), "Notification has been sent."), HttpStatus.OK);
    }

    @PostMapping("/notification/token")
    public ResponseEntity sendTokenNotification(@RequestBody PushNotificationRequest request) {
        pushNotificationService.sendPushNotificationToToken(request);
        return new ResponseEntity<>(new PushNotificationResponse(HttpStatus.OK.value(), "Notification has been sent."), HttpStatus.OK);
    }

    @PostMapping("/notification/data")
    public ResponseEntity sendDataNotification(@RequestBody PushNotificationRequest request) {
        pushNotificationService.sendPushNotification(request);
        return new ResponseEntity<>(new PushNotificationResponse(HttpStatus.OK.value(), "Notification has been sent."), HttpStatus.OK);
    }

    @GetMapping("/notification")
    public ResponseEntity sendSampleNotification() {
        pushNotificationService.sendSamplePushNotification();
        return new ResponseEntity<>(new PushNotificationResponse(HttpStatus.OK.value(), "Notification has been sent."), HttpStatus.OK);
    }
}

This is my Notification Parameter-

public enum NotificationParameter {
    SOUND("default"),
    COLOR("#FFFF00");

    private String value;

    NotificationParameter(String value) {
        this.value = value;
    }

    public String getValue() {
        return this.value;
    }
}   

This is my PushNotificationRequest-

public class PushNotificationRequest {

    private String title;
    private String message;
    private String topic;
    private String token;

    public PushNotificationRequest() {
    }

    public PushNotificationRequest(String title, String messageBody, String topicName) {
        this.title = title;
        this.message = messageBody;
        this.topic = topicName;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getTopic() {
        return topic;
    }

    public void setTopic(String topic) {
        this.topic = topic;
    }

    public String getToken() {
        return token;
    }

    public void setToken(String token) {
        this.token = token;
    }
}
    

This is my push notification Response-

package com.example.MyFirstPushNotificationService.PushNotificationsDemo;

public class PushNotificationResponse {

    private int status;
    private String message;

    public PushNotificationResponse() {
    }

    public PushNotificationResponse(int status, String message) {
        this.status = status;
        this.message = message;
    }

    public int getStatus() {
        return status;
    }

    public void setStatus(int status) {
        this.status = status;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

And this is my application-properties:

app.firebase-configuration-file=google/push-notifications-example-firebase-adminsdk.json
app.notifications.defaults={topic: 'common', title: 'Common topic - Hello', message: 'Sending test message \uD83D\uDE42', token: 'ss22t03wz208eg:APA2idkkow223FE_0v5yHxqCLTyxAQafj6nWaqi4QzwZTW004q1PUux63UsFN', payloadMessageId: '123', payloadData: 'Hello. This is payload content.'}

Please forgive me,as i am still a beginner in Fire base.....I am not getting where I am gong wrong....I think its in application properties.....Also I am getting the error at-FirebaseMessaging.getInstance().sendAsync(message).get(); of FCMService class.
Thanks in Advance

I was having same error, try debugging initialize() method in FCMInitializer.java, in my case it was having wrong JSON file path, after providing correct path, issue was resolved.

I hope to arrive on time, I had the same problem and my solution was to put the authentication that the firebase console suggests.

@Service
public class FCMInitializer {

Logger logger = LoggerFactory.getLogger(FCMInitializer.class);

   @PostConstruct
    public void initialize() {
        try {
        	FileInputStream serviceAccount =
        			  new FileInputStream("path/to/serviceAccountKey.json");

        			FirebaseOptions options = new FirebaseOptions.Builder()
        			  .setCredentials(GoogleCredentials.fromStream(serviceAccount))
        			  .setDatabaseUrl("https://your-project.firebaseio.com")
        			  .build();

        			FirebaseApp.initializeApp(options);
        } catch (IOException e) {
            logger.error(e.getMessage());
        }
    }

}

enter image description here

Add @DependsOn("fCMInitializer") to services that depend on Firebase.
Example:

@Service
@DependsOn("fCMInitializer")
public class PushNotificationService

The problem is with the file path to the Firebase SDK Admin JSON file.

To fix the error the location of the JSON file should have been target/classes/<File name here>.json as this is the canonical place where Maven puts resource files after processing.