E-Wallet Microservices

A course project✓ — verifiable claim, show the receipt (the package path is org/gfg, so this came out of a GeeksforGeeks-style curriculum), built solo. It decomposes a digital wallet into four Spring Boot services — user, wallet, transaction, and notification — communicating asynchronously over Kafka instead of direct HTTP calls between them.

Design decisions worth naming

Each service owns its own data: separate repositories, separate DTO sets, nothing shared through a common entity. The wallet service runs two distinct consumers — one for wallet-creation events, one for transaction-update events✓ — verifiable claim, show the receipt — each with its own consumer group and deserializer, so the two event types can be processed and scaled independently rather than sharing one queue. Pre-transaction user validation sits in front of the transaction path, guarding against moving money for a user in a bad state.

What's missing

Named honestly, not discovered by an interviewer: there's no docker-compose.yml, so running Kafka, MySQL, and four services locally takes manual setup. And there's no idempotency key or dead-letter handling on the consumers✓ — verifiable claim, show the receipt — if a transaction-update event replays, nothing today stops a double-credit. For a real wallet, that's the first thing I'd fix.