Flash Sale Engine

A high-concurrency flash sale backend built using Java, Spring Boot, PostgreSQL, and Redis.

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Tech Stack

• Java 21
• Spring Boot
• PostgreSQL
• Redis
• Docker
• Maven
• JPA / Hibernate

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Features

• User registration and management
• Product creation and inventory management
• Redis-based inventory caching
• Atomic inventory decrement
• Overselling prevention
• Duplicate purchase prevention
• Idempotent purchase requests
• Distributed rate limiting
• Global exception handling

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Architecture

Client
   ↓
Spring Boot API
   ↓
Redis
   ├── Inventory
   ├── Rate Limiting
   ├── Idempotency
   └── Purchase Locks
   ↓
PostgreSQL
   ├── Users
   ├── Products
   └── Orders

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Project Structure

src/main/java/com/flashsale
│
├── config
├── controller
├── dto
├── entity
├── exception
├── repository
└── service

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Prerequisites

• Java 21
• Docker Desktop
• Maven
• PostgreSQL
• Redis

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Running the Project

Start Infrastructure

docker compose up -d

Run Application

mvn spring-boot:run

Application runs on:

http://localhost:8080

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API Endpoints

Users

Create User

POST /users

Example:

{
  "name": "Alice",
  "email": "alice@test.com"
}

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Products

Create Product

POST /products

Example:

{
  "name": "PS5",
  "description": "Gaming Console",
  "price": 499.99,
  "inventory": 5
}

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Purchase

Purchase Product

POST /purchase

Example:

{
  "userId": "USER_ID",
  "productId": "PRODUCT_ID",
  "idempotencyKey": "purchase-123"
}

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