E-Commerce Backend

Introduction

Build a full e-commerce backend — product catalog, shopping cart, checkout, order processing, inventory and JWT authentication. This is the capstone project that ties together everything in the course.

Informative example

Checkout flow:

@Transactional
public Order checkout(Long userId, CheckoutRequest req) {
    Cart cart = cartService.getActive(userId);
    inventoryService.reserve(cart.items());       // fail fast if OOS
    Order order = orderRepo.save(cart.toOrder());
    paymentService.charge(order, req.paymentMethod());
    cartService.clear(userId);
    eventPublisher.publish(new OrderPlacedEvent(order));
    return order;
}

Best practices

• Separate catalog, cart, order and payment into bounded services (or modules).
• Use @Transactional for checkout — all-or-nothing.
• Publish domain events (Kafka/RabbitMQ) for order fulfillment.

Purpose of this lesson

Master E-Commerce Backend so you can apply it confidently in production Java code, technical interviews, and code reviews.

Step-by-step explanation

1. Understand the core idea behind E-Commerce Backend.
2. Walk through the runnable example and tweak it in the playground.
3. Apply the pattern in a small Spring Boot or CLI exercise of your own.
4. Re-read the common mistakes and interview Q&A to lock the concept in.

Interactive workflow diagram

Debugging tips

• Read the full stack trace — Java's exception messages name the offending class and line.
• Reproduce in the smallest possible main() method before fixing in the real app.
• Use IntelliJ's debugger breakpoints and 'Evaluate Expression' rather than scattering System.out.

Optimization strategies

• Profile before optimizing — JFR (Java Flight Recorder) and async-profiler reveal real hotspots.
• Prefer immutable data and stream pipelines over hand-rolled loops when readability matters.
• Reach for the right JDK collection (ArrayList vs LinkedList vs ArrayDeque) before writing custom data structures.

Enterprise example

This is the portfolio project that gets interviews — deploy on Railway/Fly.io with Docker Compose.

Interview questions & answers

Summary

In this lesson you learned E-Commerce Backend — the concept, syntax, a runnable example, and the production pitfalls to avoid. Apply it in the playground before moving on.