Discover Hexagonal Architecture to create web applications with isolated, testable layers. Gain insights into designing clean, maintainable modules and advocating for suitable techniques for your application.

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This course will teach you all about creating a web application in the Hexagonal Architecture style. Hexagonal Architecture promotes the separation of concerns by encapsulating logic in different layers of the application. This enables a higher level of isolation, testability, and control over your business specific code. 

You will learn how to design software modules and complete applications in a clean and maintainable manner, while also learning how to advocate for a certain technique given your application and constraints.

By the end of this course, you will have a greater understanding of how to implement software architecture, a key skill for any senior developer.

Hexagonal Software Architecture for Web Applications

# Deadline

The word “deadline” probably [originated from the 19th century](https://www.merriam-webster.com/words-at-play/your-deadline-wont-kill-you) and described a line drawn around a prison or a camp of prisoners. A prisoner that crossed that line was shot. Think about this definition the next time someone “draws a deadline” around you; it will undoubtedly open up new perspectives.

# BuckPal

A quick online search has revealed that a company called PayPal has stolen my idea and even copied part of the name. Shame on them! Joking aside, try to find a name similar to "Paypal" that is not the name of an existing company. It's hilarious!

# Any dependency

We can only invert dependencies when we have control over the code on both sides of the dependency. If we have a dependency to a third-party library, we cannot invert it since we don't control the code of that library.

# Hexagonal source
The primary source for the term "Hexagonal Architecture" seems to be an article on Alistair Cockburn's [website](https://alistair.cockburn.us/hexagonal-architecture/).

# Locking

The use case would also have to make sure that no other money transfer to and from the source and target account is happening at the same time to avoid overdrawing an account. 

# 30000 lines

It was actually a conscious architecture decision (by our predecessors, mind you) that led to those 30000 lines being in a single class. To change the system at runtime without redeployment, it allowed to upload compiled Java bytecode in a `.class` file, and it only allowed upload of *a single file*, so this file had to contain all the code.

# JPA

Does that sound familiar to you? You choose #key# JPA: Java Persistence API #key# as an OR mapper because it's the thing people use for this problem. A couple months into development you curse eager and lazy loading and the caching features and wish for something simpler. #key# JPA: Java Persistence API #key# is a great tool, but for many problems, simpler solutions may be, well, simpler.

# Mystic

This method is just a placeholder for any bootstrapping logic that is necessary to expose our web adapters via #key# HTTP: Hypertext Transfer Protocol #key#. We don’t really want to implement this ourselves.

# Shortcuts

Imagine this sentence in a book about construction engineering or, even scarier, in a book about avionics! Most of us, however, are not building the software equivalent of a skyscraper or an airplane. And software is soft and can be changed more easily than hardware, so sometimes it’s actually more economic to (consciously!) take a shortcut first and fix it later (or never).

# Personality

I'm the "Defender" personality type, and if I were a dog, I would apparently be a Pit Bull.



Before We Begin

What's Wrong with Layers?

Inverting Dependencies

Organizing Code

Implementing a Use Case

Implementing a Web Adapter

Implementing a Persistence Adapter

Testing Architecture Elements

Mapping Between Boundaries

Assembling the Application

Enforcing Architecture Boundaries

Taking Shortcuts Consciously

Assessment

Conclusion

Appendix

Appendix I

Deadline