Vijay Kumar

Production-deployed multiplayer game backend with real-time session management, persistent game state, and a full authentication pipeline. Designed, built, and shipped end-to-end as an independent engineering project.

• Concurrent game state managed via ConcurrentHashMap with atomic operations, handling simultaneous WebSocket sessions without data races
• WebSocket session lifecycle implemented with STOMP over SockJS, including connect/disconnect presence tracking and room-scoped message routing
• Diagnosed and fixed a JPQL enum inner-class reference crash (User$UserStatus) causing game move rejections every 10 seconds; resolved by passing enum as a named parameter instead of inline reference
• Resolved a Railway port-587 SMTP block by replacing JavaMailSender with Resend HTTP API on port 443, restoring account activation delivery from a 2-minute timeout to under 1 second
• CI/CD pipeline via GitHub Actions: builds JAR, copies via SCP to Oracle Cloud VM, and restarts the systemd service — zero-touch deploys
• Authentication pipeline: bcrypt password hashing, Spring Security with JWT tokens, email-based account activation with expiring tokens stored in PostgreSQL

• Built a TCP socket-based multiplayer server from scratch using raw Java Sockets, handling concurrent sessions with dedicated per-client threads and synchronized game state
• Informed the session management and concurrency design of the Nexus WebSocket platform through direct architectural iteration

• Implemented Trees, Graphs, Linked Lists, and sorting algorithms with documented time and space complexity analysis per solution

• Built and deployed a full portfolio with blog system, contact form, and responsive design using vanilla HTML/CSS/JS — no frameworks
• Backend contact API on Spring Boot with Brevo email integration, deployed on Render with environment-driven configuration