Java & Spring Boot Practice

A workspace of backend and OOD/LLD exercises in Java, built while strengthening Spring Boot, concurrency-safe persistence, and object-oriented design skills.

Highlights

Order & Inventory Management System (InventoryManagement_SpringBoot/)

A Spring Boot 3 / Java 17 backend for managing product inventory and order lifecycles.

• Layered architecture (Controller / Service / Repository) over Spring Data JPA
• Optimistic locking (@Version) on Order and Product entities to prevent lost updates under concurrent requests
• JWT-based authentication
• Redis caching (cache-aside) added on top of the base implementation to cut repeated-read latency
• REST API for products and orders, with stock validation and a NEW -> EXECUTED -> CANCELLED order state machine
• Iterated in three stages, kept as separate folders: base MVC, then +JWT, then +JWT+Redis

Parking Lot (ParkingLot/)

A low-level design exercise: a multi-class parking lot system (ParkingLot, SlotManager, Ticket, PaymentManager, pluggable PaymentMethod implementations for UPI/credit card, vehicle types) -- practicing interface-based OOP design rather than a single-file script.

jwt-demo (jwt-demo/)

A minimal Spring Boot project scaffolded to isolate and practice JWT authentication.

E-commerce experiments

E-commerce1 and E-commerce2 -- full-stack (backend + frontend) practice builds.

Fundamentals

practice, exceptionHandling, synchronisationAndMulti-threading* -- core Java exercises (collections, exception handling, basic thread synchronization).

Note on structure

This repository holds several independent practice projects rather than a single application. The Order & Inventory Management System is the most complete and is the one worth reviewing first.

Tech

Java 17, Spring Boot 3.2, Spring Data JPA, Spring Security (JWT), Redis, H2/MySQL, Maven.