Anatomy of a Spring Boot App with Clean Architecture

Steve Pember - Stavvy

In my years of experience, Clean Architecture and its inspirations have been the easiest way to create readable, flexible codebases that can be worked on by large teams. This will be a good introductory talk with example code that attendees can reference at a later date.

We as an industry often talk quite a bit about the design of platform: the high-level architectures involving microservices, distributed systems, etc. But what about the internal architecture of a given application? How can one prevent their individual codebases from becoming the muddiest of mud balls?

Over the years we have found great success in keeping our codebases coherent and straightforward by following many of the principles of Clean Architecture - which itself can be considered an evolution of “Ports and Adapters”, and “Hexagonal Architecture”. Its main concept is that a given system must be imagined as Layers of ‘circles’ with a Dependency Rule which states that code dependencies many only point inwards; outer layers may call inner layers, but inner layers know nothing of the outer layers. These layers and their relationship rules give clear guidelines on where different code should live. This keeps your core business logic independent of and agnostic to the Details. Which database are we using to store “User” entity records? Which third-party service are we using for Authorization? While important, these Details are not the concern of your core business logic. They can be swapped in and out by implementing an interface; these concerns do not and can not pollute the rest of your core business logic. If followed correctly, the end result is a clearly structured, easily testable application, that is quick to react when external details need to change.

In this presentation we will present the general philosophy of Clean Architecture, Hexagonal Architecture, and Ports & Adapters: discussing why these approaches are useful and general guidelines for introducing them to your code. Chiefly, we will show how to implement these patterns within your Spring (Boot) Applications. Through a publicly available reference app, we will demonstrate what these concepts can look like within Spring and walkthrough a handful of scenarios: isolating core business logic, ease of testing, and adding a new feature or two.