Notification Service

The Notification Service is responsible for delivering alerts and updates to users via various channels such as email, SMS or internal systems (Kafka).

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Technologies

• Java 21
• Spring Boot 3.4.4
• Kafka (consuming event messages)
• Spring Mail (optional for email)
• SLF4J + Logback (logging)
• Prometheus + Grafana (observability)

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Purpose

Service listens to Kafka topics like:

• user-logged-in-event-topic
• weather-data-event-topic

And performs actions such as:

• Send email notifications
• Log or store alerts
• Update internal dashboards

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Kafka Listener Example

@KafkaListener(topics = "user-logged-in-event-topic", groupId = "user-logined-events")
public void handleUserRegistration(UserRegisteredEvent event) {
    notificationService.sendWelcomeEmail(event.getEmail(), event.getUsername());
}

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Sending Emails

config:

spring:
  mail:
    host: smtp.example.com
    port: 587
    username: email
    password: password
    properties:
      mail.smtp.auth: true
      mail.smtp.starttls.enable: true

@Service
public class EmailService {
    private final JavaMailSender mailSender;

    public void send(String to, String subject, String text) {
        SimpleMailMessage message = new SimpleMailMessage();
        message.setTo(to);
        message.setSubject(subject);
        message.setText(text);
        mailSender.send(message);
    }
}

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Monitoring

Expose metrics at:

/actuator/prometheus

And track

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Future Improvements

• Add WebSocket notifications
• Retry failed deliveries
• Store alerts in database
• Multi-language support
• Notification templates (Thymeleaf / Markdown)