Hexagonal Architecture

Package Structure

src/main/java/com/example/
├── domain/                     ← Pure Java. Zero framework dependencies.
│   ├── model/                  ← Entities, value objects, aggregates
│   ├── port/
│   │   ├── in/                 ← Use case interfaces (driving ports)
│   │   └── out/                ← Repository/external interfaces (driven ports)
│   └── service/                ← Domain services (pure business logic)
├── application/                ← Orchestrates use cases. Spring allowed here.
│   └── usecase/                ← @Service implementations of domain ports
└── infrastructure/             ← All framework/DB/HTTP details
    ├── persistence/            ← JPA adapters implementing out ports
    ├── web/                    ← REST controllers (driving adapters)
    └── external/               ← HTTP clients, messaging adapters