So the SimulatedUser sends commands to the IReactToCommands port. The developers meet and draw the following diagram:

It's ok to 'simulate' the user at first, i.e.

When the user asks for a poem in a specific language, the system displays a random poem in that language in the console.

I want to read at least one poem each dayĪs acceptance criteria, the team agrees on: The product owner and the developers agree on the following user story: The company FooBars.io decides to build a Poetry App. Then we switch to Spring Boot and Spring MVC. We start with a simple version of the application that prints to the console.

We go all the way from a user story to a domain model inside the hexagon. I show you how to implement that application. That's why SpringMvcPublisher is called a driven adapter. This time, the hexagon calls the adapter through the port. On the right side, the SpringMvcPublisher adapter implements the IWriteLines port. Its implementation is inside the hexagon. IReactToCommands is called a driver port. Because it actively uses the port, it's called a driver adapter. The PoemController is a regular Spring MVC Controller. The PoemController adapter on the left receives requests and sends commands to the IReactToCommands port. It shows Spring MVC technology as boxes with dotted lines, ports and adapters as solid boxes, and the hexagon without its internals:Īn adapter translates between a specific technology and a technology free port.

They do not depend on web technology to drive them, for example. It enables writing fast, stable tests for the business logic. Isolating business logic inside the hexagon has another benefit. By changing the implementation of a port, you change the technology. The outside of the hexagon talks with the inside only by using interfaces, called ports. Anything inside the hexagon must be free from technology concerns. You want to use a database, instead of storing data in files? Again, write an adapter for it.ĭraw a boundary around the business logic. You want to change to a different framework? Write a new adapter. A hexagonal architecture simplifies deferring or changing technology decisions.

Hexagon eam