Integrated Kafka into a Spring Boot microservice to consume and deserialize high-volume transaction messages using a configurable topic and embedded Kafka test framework. Implemented transaction validation, entity modeling, persistence, and user balance updates using Spring Data JPA and H2. Integrated an external Incentive REST API with RestTemplate into transactional workflows. Exposed a Spring REST controller for querying user balances with JSON responses, and verified end-to-end behavior using Maven tests and debugger-driven inspection across messaging, database, and external API interactions.