Coffee Machine Simulator ☕

A Kotlin + Spring Boot hexagonal-architecture playground that simulates an espresso machine. It ships with a CLI, an in-memory H2 database, and Flyway migrations for schema + seed data.

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Disclaimer

This project is created purely for educational purposes. It is not a production-ready application and should not be used as such. The goal is to explore how Kotlin, Spring Boot, Hexagonal Architecture, and Domain-Driven Design (DDD) principles can work together in practice.

A few important notes:

• Pragmatism vs. purity: In real projects, I’d often lean on Spring annotations in the application layer for simplicity. Here, I intentionally avoided them to keep the architectural layers cleanly separated. The same applies to the idea of a dedicated bootstrap module: while more “pure,” it would force integration tests into a separate module. For practicality, I kept them in the adapters module.
• Front-end: I’m not a front-end developer. Any UI work included (or added in the future) is assisted by AI.
• Coffee expertise: I’m no barista! If you notice inaccuracies in the recipes or brewing process, I’d love your feedback.

With that in mind, enjoy!

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Getting Started

Prerequisites

• Java 21
• Gradle 8.x

Running the CLI

To run the command-line interface:

./gradlew :coffee-machine-adapters:bootRun --args='--spring.profiles.active=cli'

You should see the following prompt:

INFO  Coffee Machine CLI ☕️
INFO  Commands:
  help                          - show this help
  quit                          - exit
  power on|off                  - turn machine on/off
  status                        - show machine status
  recipes                       - list available recipes
  brew <RECIPE_NAME>            - brew a recipe (e.g., ESPRESSO)
  refill water [ml]             - refill water tank (full if ml omitted)
  refill beans [g]              - refill bean hopper (full if g omitted)
  refill waste                  - empty waste bin
INFO  > 

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Architecture & Modules

This project follows a clean, hexagonal architecture. For detailed information, please see the README.md file in each module:

• coffee-machine-domain/: Contains the core domain logic, entities, and value objects.
• coffee-machine-application/: Orchestrates the domain logic to fulfill application use cases.
• coffee-machine-adapters/: Provides the technology-specific implementations for input (CLI) and output (H2 database).

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H2 Console

If you run the application with the default profile (without --spring.profiles.active=cli), the H2 database console will be available at:

• URL: http://localhost:8080/h2-console
• JDBC URL: jdbc:h2:mem:coffee-db
• Username: sa
• Password: (empty)

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Contributing

PRs are welcome! Please see the Contributing Guide for details on how to get started.