This repository provides practical examples and code snippets to help Java developers implement effective architectural concepts and design patterns with a main focus on performance, scalability, and resiliency as primary quality attributes.
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Among the architectural styles, design tactics, and patterns demonstrated in this project:
- Layered architecture, Hexagonal architecture, Event-driven microservices architecture
- API-driven development approach
- Schema-first development approach
- Shared-nothing database approach
- Schema registry
- REST architectural style (e.g., RESTful APIs)
- Scalability (e.g., horizontal scalability)
- Location decoupling
- Resiliency
- Caching (e.g., local/embedded)
- Asynchronous logging
- Change data capture design pattern
- Listen to yourself design pattern
- Data transfer object enterprise application pattern
The purpose of this application is to have a platform where customers can find products, shop around using a cart, check out the products and initiate payments.
Below is a breakdown and description of each module in the current project.
| Module | Description |
|---|---|
Account service |
Manages user data and exposes a GraphQL interface for retrieving accounts. It includes a prefilled user account for demonstration purposes. |
Product service |
Manages the product catalog and exposes an API to create, retrieve, update, and delete products. It includes a prefilled product catalog for quick setup. |
Shopping cart service |
Manages the user's shopping cart, exposing an API to create, retrieve, update, delete, and check out items in the cart. |
Order service |
Manages user orders and provides an API to retrieve historical orders and update them as needed. |
Payment service |
Processes payments for orders using an external payment system. |
Shipping service |
Simulates the shipment of successful orders to their destination after payment processing is completed. |
Notification service |
Logs all received events to the console for monitoring and debugging purposes. |
Message schema library |
Contains AVRO message definitions used across services to ensure consistent data formats. |
End to end sequence diagram:
sequenceDiagram
actor User
User->>Product Service: Get Products
User->>Shopping Cart Service: Save Products In Cart
User->>Shopping Cart Service: Checkout Cart Items
Shopping Cart Service->>Order Service: Publish Order Created Event
Order Service->>Payment Service: Trigger Payment Command
critical Payment
Payment Service->>Payment Gateway: Trigger Payment
Payment Gateway-->>Payment Service: Payment Status (e.g., APPROVED/FAILED)
end
Payment Service-->>Order Service: Publish Payment Status Updated Event
Order Service->>Notifications Service: Publish Payment Status Updated Event
alt Payment APPROVED
Order Service->>Shipping Service: Trigger Shipping Command
Shipping Service-->>Order Service: Publish Shipping Status Updated Event (e.g., IN_PROGRESS)
critical Shipping
Shipping Service->>Shipping Gateway: Trigger Shipping
Shipping Gateway->>Shipping Service: Shipping Status (e.g., COMPLETED/FAILED)
end
Shipping Service-->>Order Service: Publish Shipping Status Updated Event (e.g., COMPLETED/FAILED)
Order Service->>Notifications Service: Publish Shipping Status Updated Event
end
Events state diagram:
stateDiagram-v2
[*] --> NEW
NEW --> PAYMENT_APPROVED
NEW --> PAYMENT_FAILED
PAYMENT_FAILED --> [*]
PAYMENT_APPROVED --> SHIPPING_IN_PROGRESS
SHIPPING_IN_PROGRESS --> SHIPPING_COMPLETED
SHIPPING_IN_PROGRESS --> SHIPPING_FAILED
SHIPPING_FAILED --> [*]
SHIPPING_COMPLETED --> [*]
Among the technologies, frameworks, and libraries included in this project:
- Spring Boot
- JdbcTemplate (e.g., query, update, batch update)
- Caffeine caching
- Kafka
- PostgreSQL
- Flywaydb
- Debezium
- Testcontainers
- Resilience4j (e.g., circuit breaker, bulkhead)
- Traefik (i.e., HTTP reverse proxy and load balancer)
- AVRO and JSON data format
- OpenAPI specification
- GraphQL
- Logback
- Spotless code formatter
- Docker compose
- ArchUnit
Please make sure you have properly installed (and configured):
- JDK 21 (i.e., latest LTS)
- Docker
- cURL
- Postman
./mvnw clean package
Note: Please start the Docker agent up front, otherwise, the tests fail.
./bootstrap.sh
To check if all Docker containers are up and running execute the below command:
docker ps -a
Important: On Windows using Docker compose v2 there is a known limitation while horizontally scaling a service by using port ranges like "8080-8081:80".
At the moment, the workaround is to simply copy-paste (multiple times) the same service inside the Docker compose YAML file and explicitly assign different ports to each.
The PostgreSQL connector is used to monitor and record the row-level changes in the PostgreSQL database schema.
Note: please make sure all services (e.g., PostgreSQL and Kafka) are up and running before registering the connector
./debezium-register-postgres.sh
Once the PostgreSQL connector is successfully registered, it reads the database log and produces events for row-level INSERT, UPDATE, and DELETE operations, emitting such events to the Kafka topic (in this case to the ecommerce-product-cdc-topic).
Open a browser and navigate to http://localhost:26060 to access the Traefik UI (it shows endpoints, routes, services, etc.).
Open a browser and navigate to http://localhost:19000 to access the Kafdrop UI (it shows topics, partitions, consumers, messages, etc.).
Open a browser and navigate to http://localhost:18080 to access the Debezium UI (it shows the PostgreSQL connector).
Open a browser and navigate to http://localhost:55080/graphiql?path=/graphql to access the GraphiQL in-browser tool for writing, validating, and testing GraphQL account-service queries.
- open Postman
- import the provided API collections, corresponding to each project, as follows:
./ecommerce-app/order-service/postman./ecommerce-app/product-service/postman./ecommerce-app/shopping-cart-service/postman
- to simulate a basic test scenario please trigger the below requests (in this sequence):
GET http://localhost:{{port}}/products
POST http://localhost:{{port}}/cart/{{userId}}/items
POST http://localhost:{{port}}/cart/{{userId}}/checkout
GET http://localhost:{{port}}/orders/{{userId}}/history
Note: the ports (i.e., service port or Traefik load balancer port) are already configured as variables in the Postman collections
A few, optional, TODOs for further enhancements might be:
- implement a scheduler to reply unprocessed/failed events
- implement API pagination
- implement database bulk updates for the remaining APIs
This project is licensed under the MIT License.
Please see the LICENSE file for full license.
/**
* eCommerce Application
*
* Copyright (c) 2022 - 2024 Ionut Balosin
* Website: www.ionutbalosin.com
* X: @ionutbalosin | LinkedIn: ionutbalosin | Mastodon: ionutbalosin@mastodon.social
*
*
* MIT License
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
*/
