SmartOrder — Part 5: The Commons Layer — Shared Infrastructure Done Right

How a carefully designed shared library eliminates boilerplate across microservices — generics, AOP logging, custom Jackson modules, and a test framework you'll wish you had years ago. Part 4 explored the Inventory Service. Before moving forward, there's a layer that quietly powers everything — a layer most tutorials skip entirely. This post dives into services/commons : the shared infrastructure that both order-service and inventory-service depend on. Commons is not a dumping ground. It's a deliberate, multi-module library that solves real problems: generic CRUD, consistent serialization, AOP-based observability, OpenAPI cleanup, and test data lifecycle management. Let's take it apart. 👉 services/commons The three sub-modules at a glance services/commons ├── commons-business ← domain-layer abstractions (no web dependency) ├── commons-service ← web-layer infrastructure (HATEOAS, Jackson, AOP) └── service-test ← test utilities with transaction control The split is intentional. commons-b