Interview Challenge

A Spring Boot backend service for managing websites, their versions, and domain mappings.

Tech Stack

• Kotlin 2.3.10
• Spring Boot 4.0.3
• PostgreSQL 16
• Gradle 9.3.1
• Java 21

Architecture

The project follows a hexagonal (ports & adapters) architecture:

core/                          # Business logic, no framework dependencies
├── {entity}/model/            # Domain models (pure data classes)
├── {entity}/port/             # Port interfaces (driven side contracts)
└── {entity}/usecase/          # Use cases (application services)

adapter/                       # Infrastructure implementations
├── {entity}/controller/       # REST controllers (driving side)
│   ├── mapper/                # Domain <-> response mapping
│   └── rest/                  # Request/response DTOs
└── {entity}/persistence/      # Database adapters (driven side)
    ├── entity/                # JPA entities
    ├── repository/            # Spring Data repositories
    ├── mapper/                # Entity <-> domain mapping
    └── impl/                  # Port implementations

Key patterns:

• Arrow Either for functional error handling (Either<Error, Success>)
• Extension functions for stateless mappers at adapter boundaries
• Sealed classes for type-safe API responses
• ArchUnit tests enforce layer dependency rules

Domain Model

• User - application user (id, email)
• Website - belongs to a user (id, user_id)
• WebsiteVersion - versioned content snapshots of a website (website_id, version_number, payload)
• Domain - domain name mapped to a website (domain, website_id)

Prerequisites

• Java 21
• Docker

Getting Started

Start the database:

docker compose up -d

Run the application:

./gradlew bootRun

The API is available at http://localhost:8080. Swagger UI is at http://localhost:8080/docs/swagger-ui.html.

Running Tests

./gradlew test

Tests use Testcontainers to spin up a PostgreSQL instance automatically — no running database required.

API Endpoints

Method	Path	Description
GET	/api/users	List users
GET	/api/users/{id}	Get user by ID
POST	/api/users	Create a user
DELETE	/api/users/{id}	Delete a user
GET	/api/websites	List websites
GET	/api/websites/{id}	Get website by ID
POST	/api/websites	Create a website
DELETE	/api/websites/{id}	Delete a website

Frontend

A React SPA that consumes the backend API. Located in the frontend/ directory.

Stack: Vite + React 19 + TypeScript + SCSS Modules + React Router 7

Setup

cd frontend
npm install

Development

npm run dev

Starts on http://localhost:3000. The Vite dev server proxies /api requests to http://localhost:8080, so make sure the backend is running.

Build

npm run build

Output goes to frontend/dist/.