Backend / API Design
Digital Wallet Platform
A layered Spring Boot service modeling wallet balances, status, and ownership.
Problem
A wallet service is a compact but complete example of backend fundamentals: it needs a clean data model (user, balance, status, identifiers, timestamps), a service layer that enforces rules about how that data can change, and a persistence layer that keeps it consistent. This project implements that end to end with a conventional, maintainable Spring Boot layering.
Architecture
Standard layered architecture: controllers stay thin and delegate to services, services own business rules (like valid wallet-status transitions), and repositories handle persistence via Spring Data JPA.
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What it does
- Wallet entity modeling: user ID, balance, wallet status, UUID identifiers, timestamps
- Clear separation between controller, service, and repository layers
- REST endpoints for wallet operations
- Persistence via Spring Data JPA / Hibernate over MySQL
Engineering decisions
UUIDs for wallet identifiers instead of sequential IDs
Avoids leaking creation order or volume through the identifier, and works cleanly if the service is ever split or scaled horizontally.
Strict layering (controller → service → repository)
Keeps business rules in one place (the service layer) so validation and status logic isn't duplicated across endpoints.
Scope note
This project does not integrate a real payment gateway and does not move real money. No such integration is claimed.