@RestController is a class-level annotation used for the resource class introduced in Spring 4. It is a combination of @Controller and @ResponseBody, and because of it, a class returns a domain object instead of a view.

In the following code, you can see that the CalculationController class handles GET requests for /calculation by returning a new instance of the calculation class.

We will implement two URIs for a Calculation resource—the square root (the Math.sqrt() function) as the /calculations/sqrt URI, and power (the Math.pow() function) as the /calculation/power URI.

The @RestController annotation helps you to add @ResponseBody and @Controller annotations to the class.

You can also import org.springframework.web.bind.annotation package in your file.

https://www.geeksforgeeks.org/spring-rest-controller/