Flight Booking Concurrency Training

This project is a concurrency exercise inspired by flight booking systems of digital airline companies. It demonstrates domain-driven design principles and concurrency control in a rich domain model.

Domain Model

Entities

Flight (Aggregate Root)

• Core entity for flight bookings
• Maintains seats and their booking status
• Ensures thread safety with ReentrantLock
• Enforces invariants:
  • Cannot book more than capacity
  • A seat can only be booked once

Booking

• Represents a passenger's booking for a specific seat
• Immutable after creation
• Links passenger, flight, and seat number

Passenger

• Represents a customer who can book flights
• Contains identification and contact information

Value Objects

FlightId

• Uniquely identifies a flight with format "EDR" followed by 5 digits
• Immutable value object

SeatNumber

• Identifies a specific seat on a flight
• Format: row number (1-99) followed by seat letter (A-F)

BookingRequest

• DTO for carrying booking request data
• Contains passenger information and desired flight

Services

BookingEngine

• Orchestrates flight bookings across multiple flights
• Provides sequential and parallel booking strategies:
  • Sequential processing
  • Parallel processing with fixed thread pool
  • Parallel processing with virtual threads (Java 21 feature)
• Tracks booking results and performance metrics

Concurrency Implementation

The project demonstrates several concurrency techniques:

1. Thread-safe entity design using ReentrantLock in the Flight entity
2. Use of ConcurrentHashMap for thread-safe collections
3. Java 21 Virtual Threads implementation
4. Traditional ExecutorService with fixed thread pool
5. Atomic operations and concurrent collections

Running the Project

Requirements

• Java 21
• Maven

Build the Project

mvn clean package

Run Tests

mvn test

Performance Comparison

The project includes performance tests comparing:

• Sequential booking
• Fixed thread pool booking
• Virtual thread booking

The ConcurrencyStressTest class demonstrates massive concurrent bookings with 10,000+ virtual threads.

Key Learning Points

• Encapsulation of concurrency inside domain objects
• Ensuring domain invariants under high concurrency
• Virtual Threads vs. platform threads performance comparison
• Thread-safe collections and their proper usage
• Designing immutable value objects

Project Structure

• src/main/java/com/edreams/booking/domain - Domain model classes
• src/main/java/com/edreams/booking/service - Service layer
• src/test/java/com/edreams/booking/domain - Unit tests for domain model
• src/test/java/com/edreams/booking/service - Service tests including stress tests