Overview

This pull request adds code examples for Chapter 13 of the MicroProfile tutorial, demonstrating practical implementation of MicroProfile Reactive Messaging 3.0.1 in a multi-service e-commerce application.

Changes

New Code Examples

Order Service (code/chapter13/order/)

• Full REST API for order management with OpenAPI documentation
• Order and OrderItem entities with Jakarta Persistence support
• In-memory repository pattern with CRUD operations
• Order status lifecycle: CREATED → PAID → PROCESSING → SHIPPED → DELIVERED
• Integration with MicroProfile Reactive Messaging for async event handling
• OrderService with transaction management and event emission
• OrderStatusEventHandler to consume payment authorization events
• NotificationService for order status change notifications

Payment Service (code/chapter13/payment/)

• Payment request processing with reactive messaging integration
• PaymentRequestHandler for consuming order-created events and emitting payment-authorized
• MicroProfile REST Client examples with multiple implementations:
  • ProductClient - Basic REST client with exception mapping
  • ProductClientWithFilters - Advanced client with authentication, correlation IDs, and logging filters
  • ProductJakartaRestClient - Low-level Jakarta REST client using ClientBuilder
• Custom response exception mappers for error handling
• Configuration source implementation for dynamic properties
• Support for both in-memory and Kafka-based messaging

API Endpoints

Order Management:

• GET /api/orders - List all orders
• GET /api/orders/{id} - Get order by ID
• GET /api/orders/user/{userId} - Get user's orders
• GET /api/orders/status/{status} - Filter by status
• POST /api/orders - Create new order
• PUT /api/orders/{id} - Update order
• PATCH /api/orders/{id}/status/{status} - Update status
• DELETE /api/orders/{id} - Delete order

Order Items:

• GET /api/orderItems/{id} - Get item
• GET /api/orderItems/order/{orderId} - Get items for order
• POST /api/orderItems/order/{orderId} - Add item
• PUT /api/orderItems/{id} - Update item
• DELETE /api/orderItems/{id} - Remove item

Configuration

• MicroProfile Config properties for Kafka connectivity
• OpenAPI annotations for automatic API documentation
• Support for both development (in-memory) and production (Kafka) deployments

Architecture Highlights

Hybrid REST + Reactive Messaging Pattern:

• REST for immediate request/response operations (checkout, queries, admin tasks)
• Reactive Messaging for asynchronous workflows (payment, inventory, shipping)

Event-Driven Workflow:

1. Shopping Cart initiates checkout via REST
2. Order Service persists order and emits order-created event
3. Payment Service consumes event and emits payment-authorized or payment-failed
4. Inventory Service consumes payment-authorized and emits reservation outcomes
5. Shipment Service consumes inventory events and manages logistics
6. Order Service normalizes all events into order-status-events for downstream consumers

Channel Definitions

• order-created - Published by Order Service, consumed by Payment Service
• payment-authorized - Published by Payment Service, consumed by Order/Inventory Services
• payment-failed - Published by Payment Service, consumed by Order Service
• inventory-reserved - Published by Inventory Service, consumed by Shipment/Order Services
• inventory-rejected - Published by Inventory Service, consumed by Order Service
• shipment-created, shipment-dispatched, shipment-delivered - Shipment lifecycle events

Design Concepts Demonstrated

• Separation of Concerns - Each microservice owns its data and lifecycle
• Scalability - Event-driven architecture allows independent service scaling
• Resilience - Async messaging decouples services, improving fault tolerance
• Developer Experience - Clean REST + Messaging patterns with full OpenAPI support

Testing & Documentation

• Comprehensive JavaDoc throughout all classes
• README files with setup and deployment instructions