A simple URL shortener

It provides:

• a REST API for creating, redirecting, listing, and deleting shortened URLs
• file-based persistence using H2
• a minimal decoupled frontend for interacting with the API
• automated tests
• Docker support for running the full application locally

• Java 17
• Spring Boot 3.5.11
• Maven
• Spring Web
• Spring Validation
• Spring Data JPA
• H2 (file-based)
• Lombok

• Node.js
• Express
• Static HTML / CSS / JavaScript

The API follows the provided openapi.yaml.

Creates a shortened URL.

Request body:

{
  "fullUrl": "https://example.com/very/long/url",
  "customAlias": "my-custom-alias"  // optional
}

Response (201 Created):

{
  "shortUrl": "http://localhost:8080/my-custom-alias" // or a randomly generated alias
}

Redirects to the original URL.

Response:

• 302 Found if alias exists
• 404 Not Found if alias does not exist

Deletes a shortened URL mapping from persistence.

Response:

• 204 No Content if deleted
• 404 Not Found if alias does not exist

Returns all shortened URLs.

Response (200 OK):

[
  {
    "alias": "my-custom-alias",
    "fullUrl": "https://example.com/very/long/url",
    "shortUrl": "http://localhost:8080/my-custom-alias"
  },
  {
    "alias": "kqmdz-plnvrtaeuw",
    "fullUrl": "https://example.org/another/long/url",
    "shortUrl": "http://localhost:8080/kqmdz-plnvrtaeuw"
  }
]

• shortUrl is not persisted
• persisted fields are:
  • alias
  • fullUrl
• shortUrl is derived as base-url + "/" + alias
• base-url is read from the environment by the APP_BASE_URL or is the default http://localhost:8080/
• example:
  • fullUrl = https://example.com/very/long/url
  • alias = my-custom-alias
  • shortUrl = http://localhost:8080/my-custom-alias

Custom aliases are optional and validated as follows:

• lowercase letters and hyphens only
• must start and end with a lowercase letter
• no consecutive hyphens
• max length: 16 characters

• DTO validation handles basic field validation
• API layer request validation checks that fullUrl is a valid absolute http or https URL
• business rules such as alias uniqueness are handled in the service layer
• API errors are returned as JSON error responses

Example error response:

{
  "error": "Alias already exists: my-custom-alias"
}

From the repository root:

docker-compose up --build

Services:

• frontend: http://localhost:3000
• backend: http://localhost:8080

The backend uses a Docker volume for H2 file persistence.

To stop containers:

docker-compose down

To stop containers and remove the persisted database volume:

docker-compose down -v

• Java 17
• Maven
• Node.js and npm

From backend/url-shortener-api/:

./mvnw spring-boot:run

can be run at the same location by:

./mvnw test

Backend runs on:

http://localhost:8080

From the frontend/ directory:

npm ci
npm start

Frontend runs on:

http://localhost:3000

and can be accessed by opening http://localhost:3000 in a browser

A minimal decoupled frontend is included, it supports:

• creating short URLs
• listing saved URL mappings
• deleting saved URL mappings
• showing API success and error messages

The frontend is served separately, the browser essentially retrieves the static web pages from the frontend docker container and calls the API directly from the browser.

• aliases are unique across all saved URL mappings.
• a url can have many aliases.
• H2 file-based persistence being sufficient for this exercise

This submission intentionally keeps the solution simple and focused on the requirements:

• manual implementation from the provided OpenAPI contract
• backend-first approach
• minimal decoupled frontend
• simple Docker setup

Time spent: approximately ~15 hours across several sessions.

curl -i -X POST http://localhost:8080/shorten \
  -H "Content-Type: application/json" \
  -d '{
    "fullUrl": "https://example.com/very/long/url",
    "customAlias": "my-custom-alias"
  }'

curl -i http://localhost:8080/my-custom-alias

curl -i http://localhost:8080/urls

curl -i -X DELETE http://localhost:8080/my-custom-alias