Architecture

Software architecture is the foundational blueprint that determines the long-term success of an application. For developers working with Spring Boot, architectural choices have a direct impact on maintainability, scalability, and overall development productivity. A poorly chosen structure can result in a codebase that is hard to test, expensive to modify, and slow to evolve. Among the available patterns, Three-Layer Architecture and Clean Architecture are two of the most frequently used approaches. The former emphasizes simplicity and delivery speed, while the latter focuses on domain-centric design and long-term flexibility. This guide provides a clear, comparative analysis of both architectures, complete with practical examples, to help teams make informed decisions based on their project’s goals and constraints.

Hexagonal Architecture (HA), also known as Ports and Adapters Architecture, is a foundational and influential software design pattern, first introduced by Alistair Cockburn in 2005.

The term “Hexagonal Architecture” comes from a visual convention: the application component is drawn as a hexagon, not to imply it must have six boundaries or ports, but to leave enough space to represent the different interfaces connecting the component to the outside world. As Cockburn stated in his 2005 article:

The hexagon is not a hexagon because the number six is important, but rather to allow the people doing the drawing to have room to insert ports and adapters as they need, not being constrained by a one-dimensional layered drawing.

This insight is crucial—it reminds us to stop focusing on the shape and instead focus on the core concept: defining the application’s API via ports and connecting it to the outside world with interchangeable adapters. This shift from diagram to intent is the first step toward architectural maturity.

Ports & Adapters (Hexagonal Architecture) explicitly defines two layers: the inside (application core) and the outside (everything else), and requires clear definition of ports for interaction.

(Clean Architecture builds on this by further splitting the application core into more granular layers such as Use Cases, Entities, and Domain Services, but is less prescriptive about the “port” metaphor for the outer boundary.)