Christopher Flynn

Turning ideas into products, and code into impact—building scalable systems that power real-world solutions.

1 minute read

Link to Project

FairSplit is a full-featured expense splitting app that allows users to create groups, log shared expenses, and track who owes who. Built from scratch using Java and Spring Boot on the backend and React with Tailwind on the frontend, it supports JWT authentication, real-time balance calculations, and full CRUD functionality.

The Goal

Create a modern, real-world full-stack web app with:

  • Secure registration and login using JWT
  • Group creation and invite-based joining
  • Adding shared expenses with custom splits
  • Calculating live balances and settlement flows
  • Clean, responsive frontend with Tailwind CSS
  • Production deployment with Docker, Render, and Netlify

Stack Overview

Layer Tools
Frontend React + Vite + Tailwind CSS v4
Backend Spring Boot + Gradle + JWT
Database PostgreSQL (via Render)
Deployment Backend on Render, Frontend on Netlify
Auth JWT token-based auth
DevOps Dockerfile + CI/CD + environment vars

Core Features

  • JWT Authentication: Secure login and protected routes
  • Groups: Create, join via invite code, and manage
  • Expenses: Add expenses, split between users, calculate who owes whom
  • Balances: Auto-calculate real-time balances with custom logic
  • Settlement Suggestions: Show users how to settle up (one-to-one)
  • UI Polishing: Tailwind-based styling, component architecture, responsive layout

Challenges Faced

  • Settlements logic: Designing a reliable way to resolve debt into simple payback suggestions
  • CORS woes: Handling cross-origin requests between Netlify and Render (solved via config)
  • JWT debugging: Tracking down subtle token bugs during auth routing
  • Database setup: Using Flyway migrations to bootstrap cloud DB cleanly
  • Dark mode regrets: Started, then scrapped — next version maybe

Deployment Notes

  • Spring Boot backend containerized and deployed to Render via Docker
  • PostgreSQL provisioned via Render’s managed DB
  • React frontend deployed to Netlify with VITE_API_URL as an env var
  • Netlify _redirects file added to support SPA routing

What I Learned

  • How to build a scalable backend in Java with clean service/repo structure
  • Deploying full-stack apps with Docker and cloud CI/CD
  • Advanced CORS and JWT session handling across domains
  • Tailwind v4 workflows in production-grade projects
  • Real-world team-friendly folder structure and DTO/service isolation

Try It Out

Live App
GitHub Repo

FairSplit isn’t just a demo — it’s a deployable, usable full-stack application with clean architecture, production hosting, and sharp UI. It’s the foundation for more advanced apps to come, and a concrete example of what I can build from scratch and take all the way to production.

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