Mini Expense Manager Tech Stack React + TypeScript, Spring Boot, PostgreSQL

Setup

Frontend: Create React app (Vite) Place files from frontend folder

npm install npm start

Backend: Create DB: expense_db

Update credentials in application.properties Run Spring Boot app (port 8081)

Design Note

I implemented rule-based categorization using a simple vendor-to-category mapping in the service layer (e.g., Swiggy → Food).

During expense creation and CSV upload, the vendor name is matched and the category is assigned automatically.

For anomaly detection, I calculate the average expense amount per category from the database and flag any expense that is more than 3× this average.

The data model is kept simple with a single Expense table storing date, amount, vendor, category, and anomaly flag. This keeps queries and logic easy to understand for a small application.

As a trade-off, CSV parsing is basic (comma-separated without advanced validation), and the categorization rules are hard-coded instead of stored in a separate table.

The UI and validations are minimal since the focus is on backend logic and overall approach.