Infrastructure, databases, UI, and external services.
The lifestyle of an average Indian is also inextricably linked to the geography and diversity of the land. From the salt deserts of Kutch to the backwaters of Kerala, the "Indian lifestyle" varies significantly in language, attire, and cuisine. Dietary habits are perhaps the most intimate expression of this culture; the use of indigenous spices and the practice of Ayurveda suggest a lifestyle where food is viewed as both sustenance and medicine. Similarly, traditional clothing like the Saree and Kurta persists alongside Western fashion, symbolizing a society that is comfortable inhabiting two worlds at once.
your-project/ ├── domain/ (Pure Java) ├── application/ (Java + Port Interfaces) ├── infrastructure/ (Framework specifics: JPA, REST) └── bootstrap/ (Startup & Configuration)
Business logic can be tested in isolation without needing a database or UI.
The absolute center of your application. It contains pure business logic, rules, and data structures. It must remain entirely free of framework annotations like Spring or Hibernate. 2. Ports (Interfaces) Ports act as entry and exit points to the application core. Infrastructure, databases, UI, and external services
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This class contains core business rules and has no annotations from JPA or Hibernate.
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—both "Driving" (like REST APIs or CLIs) and "Driven" (like database implementations)—that connect external systems to the inner application ports. 2. Implementation Strategies Dietary habits are perhaps the most intimate expression
If your team decides to migrate from SQL to a NoSQL database, you only rewrite the Secondary Adapter layer. The core application logic remains untouched, un-retested, and completely safe.
First, we define our domain entity. It contains the business rules.
Why a hexagon? Unlike a layered architecture (which implies a strict top-to-bottom flow), a hexagon allows for multiple connection points. The core contains the domain logic. Surrounding it are , which are interfaces defining how the world interacts with the application (incoming) and how the application interacts with the world (outgoing). The hexagon has six sides, visually implying that there can be "many" ports, though in reality, you can have as many as you need.
Define how the outside world interacts with the application (e.g., executing a user command). The absolute center of your application
What or external services must your application integrate with?
Ports (interfaces) and Adapters (implementations) that connect the inside and outside.
Invented by Dr. Alistair Cockburn, the Hexagonal Architecture (also known as the Ports & Adapters pattern) is a structural design strategy designed to counter the tyranny of tight coupling. It promotes the separation of concerns by drawing a clear, uncrossable line between your core business logic and the external world (HTTP requests, databases, message queues, etc.).
Step 3: Application Service Implementation (The Core Engine)
An defines what external resources the application needs:
: The innermost layer containing core business rules through entities and value objects. It remains completely technology-agnostic and has no dependencies on other layers. Application Hexagon