Fleet Management API (VeloCity)

Spring Boot REST API for an e-bike rental platform, with a separate React / TypeScript client. Double-booking is prevented at the database level by a PostgreSQL exclusion constraint over date ranges, mapped to a clean HTTP 409 and verified by a Testcontainers concurrency test. The reservation lifecycle is a domain state machine with @Version optimistic locking against lost updates. Stateless JWT auth with a Redis-backed token blacklist for logout. BigDecimal pricing engine written test-first; 40+ tests run in GitHub Actions, and a deploy workflow ships the Docker image to Oracle Cloud.

Java 25Spring Boot 4PostgreSQLRedisLiquibaseTestcontainersDockerGitHub Actions

Live DemoAPIClient

LLM Evaluation API (MockBean)

Spring Boot + LangChain4j API that grades technical interview answers with an LLM as judge, in RAG (PostgreSQL + pgvector) or plain-prompt mode; Claude, Gemini or a local Llama 3.1 is selected via Spring profiles. Benchmarked 3 models × 2 modes on 40 labelled answers with bootstrap confidence intervals: Claude reached 92.5% accuracy, and RAG did not improve accuracy for any model. Schema managed by Flyway migrations instead of Hibernate auto-DDL; every evaluation is persisted for analysis.

Java 21Spring Boot 3LangChain4jPostgreSQLpgvectorFlywayPython

Code

E-Commerce Marketplace API (Grailkits)

Marketplace backend split into four containerized services (API Gateway, Catalog, Order, Review). Login uses Keycloak (OAuth 2.0 Authorization Code + PKCE); the gateway validates JWTs against Keycloak's JWKS and applies Redis-backed rate limiting before proxying to the services. Polyglot persistence: PostgreSQL for transactional order state, MongoDB for flexible product details and reviews.

Node.jsExpress.jsKeycloakOAuth 2.0PostgreSQLMongoDBRedisDocker

Code

Smart Home Simulator (IoT)

IoT platform that simulates smart-home hardware talking to an ASP.NET Core (.NET 10) backend over TCP and MQTT, with real-time dashboard updates via SignalR and persistence through Entity Framework Core. 83 xUnit tests (unit, integration and Reqnroll BDD) run in the GitHub Actions pipeline.

C#.NET 10EF CoreMQTTSignalRDockerxUnit

Code