💸 Expense Splitter API (Spring Boot)

A RESTful backend service to split and manage group expenses fairly — inspired by apps like Splitwise. Useful for roommates, trip planners, or friends splitting bills.

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🚀 Features

✅ Core Functionality

• Add, view, update, and delete expenses
• Supports EQUAL, EXACT, and PERCENTAGE split types
• Automatically tracks who paid and who owes
• Settlement summary with minimized transactions
• Error handling and input validation
• Extracts people from expense data (no separate user creation needed)

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📦 Tech Stack

• Backend: Java 17, Spring Boot 3
• Database: PostgreSQL (can use Railway, Render, or local setup)
• Validation: Jakarta Bean Validation
• API Testing: Postman
• Deployment: Railway / Render / any public platform

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🛠️ Setup Instructions

1. Clone the Repository

git clone https://github.com/your-username/expense-splitter-api.git
cd expense-splitter-api
2. Configure Database
Update your application.properties:

2. Configure Database

Update your application.properties:

spring.datasource.url=jdbc:postgresql://<your-db-host>/<your-db-name>
spring.datasource.username=<your-username>
spring.datasource.password=<your-password>
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

3. Build & Run

./mvnw clean install
./mvnw spring-boot:run
App will be running at: http://localhost:8080

📘 API Documentation

📁 Expense Management

➕ Add Expense

POST /expenses

{
  "amount": 600.0,
  "description": "Dinner at restaurant",
  "paidBy": "Shantanu",
  "splitType": "EQUAL",
  "shares": null
}

📝 Update Expense

PUT /expenses/{id}

Use the same request body format as POST.

❌ Delete Expense

DELETE /expenses/{id}

📄 Get All Expenses

GET /expenses

🤝 People & Settlement

👥 List All People

GET /expenses/people

💰 View Balances

GET /balances

Returns each person’s net balance (positive = owed, negative = owes)

📉 Settlement Summary

GET /settlements

Returns optimized transactions like:

[ { "from": "Sanket", "to": "Shantanu", "amount": 200 }, { "from": "Om", "to": "Shantanu", "amount": 150 } ] 🧪 Testing with Postman A public Postman collection is included with:

All required API endpoints

Sample test data

Folder organization by feature

Pre-filled users: Shantanu, Sanket, Om

🧾 Example Use Case

Add expenses:

Dinner (₹600 by Shantanu)

Groceries (₹450 by Sanket)

Petrol (₹300 by Om)

View balances:

{ "Shantanu": 400.0, "Sanket": -200.0, "Om": -200.0 } View settlement summary:

json Copy Edit [ { "from": "Sanket", "to": "Shantanu", "amount": 200 }, { "from": "Om", "to": "Shantanu", "amount": 200 } ]

🧠 Project Structure

src/main/java/com/example/expensesplitter/
├── controller
│   └── ExpenseController.java
│   └── SettlementController.java
├── dto
│   └── ExpenseDTO.java
│   └── SettlementDTO.java
├── model
│   └── Expense.java
│   └── SplitType.java
├── repository
│   └── ExpenseRepository.java
├── service
│   └── ExpenseService.java
│   └── SettlementService.java
├── exception
│   └── InvalidExpenseException.java
│   └── GlobalExceptionHandler.java
└── ExpenseSplitterApplication.java

⚠️ Known Limitations

No authentication or user sessions

Only handles basic expense logic

Floating-point rounding may affect precise totals

Frontend not included (optional)

📌 Optional Enhancements (Extra Credit)

Recurring expenses (e.g. rent, subscriptions)

Expense categories (Food, Travel, etc.)

Monthly spending reports

Web dashboard for visual summary

🙌 Contributing

Pull requests are welcome! For major changes, open an issue first to discuss what you'd like to change.

📄 License

This project is licensed under the MIT License.

🙏 Acknowledgements

Inspired by:

Splitwise

Google Pay Bill Split