Wallet Funds Transfer Service

Overview

Wallet Funds Transfer Service is a high-performance, Payment API that implements banking-grade transaction management with ACID compliance. Built with Spring Boot 3 and Java 17, it demonstrates modern backend development practices including distributed transactions, optimistic locking, and Spring security.

Features

• Atomic Money Transfers - ACID-compliant fund transfers with rollback support
• Optimistic Locking - Prevents double-spending in high-concurrency scenarios
• JWT Authentication - Stateless, secure user authentication
• Comprehensive API Docs - Interactive documentation with Swagger UI
• Docker Support - Containerized deployment with Docker Compose
• Test Coverage - Unit, integration, and concurrency tests
• Performance Optimized - Connection pooling, batch processing, and caching

Project Architecture

┌─────────────────────────────────────────────────────────────┐
│                       Client Applications                   │
└───────────────────────────────┬─────────────────────────────┘
                                │
┌───────────────────────────────▼─────────────────────────────┐
│                API Gateway (Spring Cloud Gateway)           │
└───────────────────────────────┬─────────────────────────────┘
                                │
┌───────────────────────────────▼─────────────────────────────┐
│                 Wallet Funds Transfer Service               │
│  ┌───────────────────────────────────────────────────────┐  │
│  │                   REST Controllers                    │  │
│  └───────────────┬───────────────────────┬───────────────┘  │
│                  │                       │                  │
│  ┌───────────────▼───────┐ ┌────────────▼───────────────┐   │
│  │    Account Service    │ │    Transaction Service     │   │
│  └───────────────┬───────┘ └────────────┬───────────────┘   │
│                  │                       │                  │
│  ┌───────────────▼───────────────────────▼───────────────┐  │
│  │                    Repository Layer                   │  │
│  └───────────────────────────┬───────────────────────────┘  │
│                              │                              │
└──────────────────────────────┼──────────────────────────────┘
                               │
                 ┌─────────────┴───────────────┐
                 │                             │
    ┌────────────▼───────┐        ┌────────────▼───────┐
    │   PostgreSQL DB    │        │    H2 (for dev)    │
    └────────────────────┘        └────────────────────┘

Tech Stack

• Core: Java 17, Spring Boot 3.1.0
• Security: Spring Security 6.1.0, JWT, BCrypt
• Database: PostgreSQL 15, H2 (development)
• Data Access: Spring Data JPA, Hibernate 6.2.0
• API Docs: SpringDoc OpenAPI 3.0
• Build: Maven 3.8.6+
• Containerization: Docker 20.10+, Docker Compose
• Testing: JUnit 5, TestContainers, MockMVC

Quickstart

Local Development (Database)

# Clone the repository
git clone https://github.com/yourusername/rupeexfer.git
cd rupeexfer

# Run with Maven
mvn spring-boot:run -Dspring-boot.run.profiles=dev

Access the application at http://localhost:8080

Docker with PostgreSQL

docker-compose up --build

Environment Variables

Variable	Default (Dev)	Description
SPRING_PROFILES_ACTIVE	dev	Active Spring profile
DB_URL	jdbc:h2:mem:rupeexfer	Database connection URL
DB_USERNAME	sa	Database username
DB_PASSWORD	(empty)	Database password
JWT_SECRET	your-256-bit-secret	JWT signing key
JWT_EXPIRATION_MS	86400000 (24h)	JWT expiration time in ms

API Endpoints

Method	Endpoint	Description	Auth Required
POST	/api/auth/signin	User authentication	No
POST	/api/accounts	Create new account	Yes
GET	/api/accounts/{accountNumber}/balance	Get balance	Yes
POST	/api/transactions/transfer	Transfer funds	Yes
GET	/api/accounts/{accountNumber}/transactions	Transaction history	Yes

Example Requests

1. Create Account

curl -X POST 'http://localhost:8080/api/accounts' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_JWT_TOKEN' \
  -d '{
    "accountType": "SAVINGS",
    "initialBalance": 1000.00
  }'

2. Transfer Funds

curl -X POST 'http://localhost:8080/api/transactions/transfer' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_JWT_TOKEN' \
  -d '{
    "sourceAccountNumber": "ACC123456",
    "destinationAccountNumber": "ACC789012",
    "amount": 100.00,
    "description": "Dinner bill"
  }'

3. Get Transaction History

curl 'http://localhost:8080/api/accounts/ACC123456/transactions?page=0&size=10' \
  -H 'Authorization: Bearer YOUR_JWT_TOKEN'

Testing

Run the complete test suite:

mvn test

Test categories:

• Unit tests (*Test.java)
• Integration tests (*IT.java)

Design Choices

Optimistic Locking

• Prevents lost updates in concurrent transfer scenarios
• Uses @Version for automatic conflict detection
• Throws OptimisticLockingFailureException on conflicts

ACID Compliance

• All money transfers are wrapped in @Transactional
• Automatic rollback on any failure
• Consistent state guaranteed at all times

Immutable Ledger

• All transactions are append-only
• No updates/deletes on transaction records
• Complete audit trail for compliance

Idempotency

• Support for idempotency keys in transfer requests
• Prevents duplicate processing of the same request
• Essential for reliable retries

Deployment

Build JAR

mvn clean package

Run JAR

java -jar target/rupeexfer-0.0.1-SNAPSHOT.jar

Production Deployment

For production deployment, it's recommended to:

1. Use HTTPS
2. Set strong database credentials
3. Configure proper JWT secret
4. Enable proper logging and monitoring
5. Set up proper backup strategy

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

License

Copyright © 2025 Sanket Desai. All rights reserved. This project is licensed under the MIT License - see the LICENSE file for details.