Hexagonal Architecture in Practice: Building Maintainable Systems in Java

1. Introduction

As applications scale, the need to separate concerns and ensure testability, maintainability, and flexibility becomes critical. Hexagonal Architecture (Ports and Adapters) provides a framework for cleanly structuring applications around core logic, enabling better testability and decoupling from technologies like databases and HTTP.

2. Why Hexagonal Architecture?

Problems with Layered Architecture

• Tight coupling between layers (especially business logic and persistence)
• Difficult to test core logic in isolation
• Changing frameworks (e.g., from REST to gRPC) involves deep changes

Goals of Hexagonal Architecture

• Isolate the domain logic from the infrastructure
• Allow multiple interfaces (web, CLI, batch jobs, etc.) to drive the app
• Enable easy swapping of persistence and external systems

3. Core Components

Hexagonal Architecture

Application Core (Center Hexagon):

• Contains all business logic and domain models