Notification Service

A Spring Boot microservice that accepts notification requests over HTTP, persists them in MongoDB, and processes email delivery asynchronously via RabbitMQ.

How It Works

1. A client sends a POST /api/notifications request.
2. The notification is saved to MongoDB with status PENDING.
3. A message is published to RabbitMQ.
4. A consumer picks up the message and sends the email via Mailtrap SMTP.
5. The notification status is updated to SENT or FAILED.

Failed messages are routed to a dead-letter queue for later inspection.

Tech Stack

• Java 26
• Spring Boot 4.1
• MongoDB Atlas
• RabbitMQ
• Mailtrap (SMTP)
• Maven

Prerequisites

• Java 26+
• Maven (or use the included ./mvnw wrapper)
• Docker (for local RabbitMQ)
• MongoDB connection string
• Mailtrap SMTP credentials

Getting Started

1. Clone the repository

git clone <repository-url>
cd notification-service-application

2. Configure environment variables

Copy the example env file and fill in your values:

cp .env.example .env

Required variables:

Variable	Description
MONGODB_URI	MongoDB connection string (Atlas)
MAIL_USERNAME	Mailtrap SMTP username
MAIL_PASSWORD	Mailtrap SMTP password

The app loads .env automatically via spring.config.import in application.yml. Do not commit .env — it is listed in .gitignore.

3. Start RabbitMQ

docker compose up -d

RabbitMQ will be available at:

• AMQP: localhost:5672
• Management UI: http://localhost:15672 (guest / guest)

4. Run the application

./mvnw spring-boot:run

On Windows:

mvnw.cmd spring-boot:run

The service starts on http://localhost:8080.

API Endpoints

Health check

GET /api/health

Create notification

POST /api/notifications
Content-Type: application/json

{
  "recipient": "user@example.com",
  "subject": "Welcome",
  "body": "Thanks for signing up!"
}

Response 201 Created:

{
  "id": "6a5941134a9541fd3c6b2fef",
  "recipient": "user@example.com",
  "subject": "Welcome",
  "status": "PENDING",
  "createdAt": "2026-07-16T20:37:39.148Z"
}

Get notification by ID

GET /api/notifications/{id}

Response 200 OK:

{
  "id": "6a5941134a9541fd3c6b2fef",
  "recipient": "user@example.com",
  "subject": "Welcome",
  "status": "SENT",
  "createdAt": "2026-07-16T20:37:39.148Z"
}

Ping

GET /api/ping

Notification Statuses

Status	Meaning
PENDING	Saved and queued, email not yet sent
SENT	Email delivered successfully
FAILED	Email delivery failed (see failureReason)

Configuration

Main settings live in src/main/resources/application.yml. Sensitive values are injected from .env:

spring:
  mongodb:
    uri: ${MONGODB_URI}

  mail:
    host: sandbox.smtp.mailtrap.io
    port: 2525
    username: ${MAIL_USERNAME}
    password: ${MAIL_PASSWORD}

RabbitMQ queue and exchange names are under the notification.rabbitmq prefix in application.yml.

Actuator

Health and metrics endpoints are exposed at /actuator:

• /actuator/health
• /actuator/info
• /actuator/metrics

Project Structure

src/main/java/com/mogeni/notificationserviceapplication/
├── config/          # MongoDB, RabbitMQ configuration
├── controller/      # REST endpoints
├── dto/             # Request/response objects
├── entity/          # MongoDB documents
├── exception/       # Custom exceptions
├── repository/      # Spring Data MongoDB repos
└── service/         # Business logic, producer, consumer, email

Running Tests

./mvnw test