In progress

Mini Banking Transaction System

A Spring Boot banking core that models account transfers as first-class transactions. The focus is correctness under concurrency: two users cannot double-spend the same balance, and competing updates fail safely instead of silently overwriting each other.

• Java
• Spring Boot
• Spring Data JPA
• PostgreSQL

Highlights

• Optimistic locking with JPA @Version so stale writes are rejected instead of overwriting committed balances.
• Pessimistic locking via SELECT FOR UPDATE on the rows that participate in a transfer.
• Deadlock prevention by locking accounts in a deterministic order before mutating balances.
• Service-layer @Transactional boundaries so debit and credit commit as a single atomic unit.
• PostgreSQL as the source of truth for accounts, ledgers, and transaction history.