Writing the REST controller class

You could say that Roy Fielding is the father of Representational State Transfer (REST), given that he had defined this term in his doctoral dissertation. REST is a style of software architecture that amazingly utilizes the existing HTTP/S protocols. RESTful systems comply with REST architecture properties, principles, and constraints.

Now, you'll create a REST controller to handle the Calculation resource. The REST controller class handles the HTTP requests in the Spring RESTful web service implementation.