Backend Developer Test

Build an application that provides RESTful endpoints and follows commonly understood best practices. Third party libraries are acceptable. Please note this should not have a Frontend, so no views or HTML are required.

Requirements

Endpoints

The application will provide the endpoint /articles/{id} for GET method, that will return the EnrichedArticle object that corresponds to the given {id}, represented as JSON.

Functionality

The application will attempt to get the required Article from an External Service, through a GET request to the endpoint /externalService/{id} (of a given base URL). If the external service does not provide the requested Article, then the application will query the internal database to provide it.

Finally, the Article object is wrapped within an EnrichedArticle object, which is then returned as response.

HTTP Status Codes and Exception handling

The application must handle the following exceptions:

• Bad Request: if the provided {id} is null or empty
• Not Found: if the required Article cannot be retrieved from the external service nor from the database
• Forbidden: no authorization logic is required, but the application will handle a custom ForbiddenException that could be thrown internally
• Internal Server Error: the application will handle any other exception returning Internal Server Error

Article and EnrichedArticle

The Article object can be either retrieved from the External Service or from the database, and it consists of three properties of type String, id, title and content.

The EnrichedArticle object consists of two properties, article of type Article, and referencingCities, which is a Set<String> of cities that are related to the corresponding article.

The EnrichedArticle class has a static Map<String, List<String>> which relates cities to several article Ids.

Given an article Id, the corresponding Article object will be retrieved from the External Service or from the database, then an EnrichedArticle object will be created from this Article object. The property referencingCities of the EnrichedArticle object will consist of a Set of the cities that relate to the corresponding article Id, sorted alphabetically.

Incremental design

The skeleton classes that conform the RESTful API are provided, and we suggest to follow the below steps:

1. Implement the method generateReferencingCities() of the class EnrichedArticle, so that it returns a Set of the cities that relate to the given article Id, sorted alphabetically.
2. Implement the configuration to connect to the External Service in class ApplicationConfig. Suggest to use Retrofit.
3. Implement the method getArticle(String id) of the class ExternalService, to return Optional<Article>.
4. Implement the method getEnrichedArticleById(String id) of the class ArticleController to return the ResponseEntity with the EnrichedArticle containing the Article retrieved from the External Service (if successful).
5. Implement the method getArticleById() of the class ArticleService to retrieve the Article object from the database, given its id.
6. Add the logic to the method getEnrichedArticleById(String id) of the class ArticleController to retrieve the Article from the database when the request to the external service is not successful.
7. Handle the cases of Bad Request (e.g. for a given wrong id) and Not Found.
8. Add custom exception classes within the package uk.co.devtest.exception, and add the corresponding methods in the class CustomExceptionHandler to handle these exceptions, returning the appropriate ResponseEntity (e.g. with HTTP status code Internal Server Error).
9. Modify the method getEnrichedArticleById(String id) of the class ArticleController to handle the possible exceptions.

Note: progress as far as you can following the above steps. It is not a requirement to complete all of them. We will value quality over quantity, so a good solution to part of the expected functionality is better than a poor solution to all the requirements.

Frameworks, Libraries and recommendations

• This RESTful web service has been built with Spring Boot.
• We expect the candidate to follow TDD, including at least the mot significant tests (both unit and integration tests).
• Testing can be done by using Spring Boot Test Starter, JUnit5 / JUnit4 + Hamcrest, Mockito, WireMock, MockMvc / TestRestTemplate / Rest-assured, or any other frameworks/libraries.
• As HTTP client to connect to the External Service you can use Spring's RestTemplate, Retrofit, Unirest or similar libraries.
• For database requests, we suggest to implement the service ArticleService based on the provided CrudRepository ArticleRepository, but you are free to use JDBI, JDBC or any ORM or library.

Some ideas of what we are looking for are:

• Well thought out software design.
• Testing.
• Clean code.