Spring Boot

Spring Boot is a Java framework built on Spring that simplifies application development with auto-configuration, embedded servers, and minimal boilerplate code. It helps developers build production-ready applications for web, REST APIs, microservices, security, and cloud deployment.
REST API Development
Spring Boot simplifies the creation of REST APIs using annotations and minimal configuration.
REST services exchange data in formats such as JSON and XML, with JSON being the most widely used format.
REST
REST (Representational State Transfer) is an architectural style used for designing network-based applications. It allows different systems to communicate over HTTP using standard methods such as GET, POST, PUT, and DELETE.

• Introduced by Roy Thomas Fielding to simplify web communication using HTTP protocols.
• Widely used for building scalable and stateless web APIs in frameworks like Spring Boot.

REST Controller
A REST Controller in Spring Boot is a class annotated with @RestController that processes incoming HTTP requests and returns data objects rather than views.

• It combines the functionality of @Controller and @ResponseBody.
• It is primarily used for building RESTful APIs.
• The response is automatically converted to JSON or XML using message converters.

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, Welcome to REST API!";
    }
}

• @RestController tells Spring that this class will handle REST API requests.
• @GetMapping("/hello") maps the HTTP GET request to the method.
• The method returns a String, which Spring sends directly to the client as the response.

References
https://www.geeksforgeeks.org/advance-java/spring-rest-controller/
https://www.geeksforgeeks.org/springboot/spring-boot-introduction-to-restful-web-services/
https://www.geeksforgeeks.org/springboot/introduction-to-spring-boot/