Architecture By Examples

Table of Contents

• Use case
• Usage
  • Requires
  • Build
  • Testing
• Architectures

This repository demonstrates different architectures of the same simple use case.

Use case

The application has

• one external endpoint

• one use case

• one aggregate

  • one entity

  • two value objects

• one database table

Figure 1. A single subscription use case

Database table

CREATE TABLE IF NOT EXISTS subscriptions (
	id BINARY(36) PRIMARY KEY,
	email VARCHAR(512) NOT NULL,
	status VARCHAR(256) NOT NULL,
	created_at TIMESTAMP WITHOUT TIME ZONE NOT NULL,
	version BIGINT NOT NULL
);

Usage

Requires

• Java 21

Build

• Import in your favourite IDE

• Start each project as a spring boot application individually or run ./mvnw spring-boot:run

Testing

• Go to http://localhost:8080/create

  

• Four conditions can be tested

  • empty input

    

  • not empty but invalid email format

    

  • correct email format

    

  • correct email format but duplicate

    

• To verify DB records, go to:

  URL	http://localhost:8080/h2-console
  JDBC URL	jdbc:h2:mem:testdb
  username	sa
  password	password

  

Architectures

#	Name	Architecture	Summary	Pros	Cons
1	anarchy	Anarchy Architecture	Everything is completely wrong	Job Security	Chaotic Mess
2	layered	Layered Architecture	Traditional 3-layer architecture	Simple	Poor package naming by technical functions
2	layered-ddd-1	Minimal DDD Architecture	Small Improvement of Layered Architecture	Simple	No "Modeling"
3	layered-ddd-2	DDD Architecture	More Improvement of Layered Architecture	Clear boundary	Extra complexity
5	layered-hex	Hexagonal Architecture (Ports and Adapters)	More Improvement of Layered Architecture	Clear boundary	Extra complexity
7	fn	Functional Domain Driven Design	Implement DDD using Clojure	Functional	Difficult to get start