The @Controller annotation indicates that a particular class serves the role of a controller. Spring Controller annotation is typically used in combination with annotated handler methods based on the @RequestMapping annotation. It can be applied to classes only. It's used to mark a class as a web request handler

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// Annotation

@Controller

// Main class

public class DemoController {

    @RequestMapping("/hello")

    @ResponseBody

    // Method

    public String helloGFG()

    {

        return "Hello GeeksForGeeks";

    }

}

https://www.geeksforgeeks.org/spring-controller-annotation-with-example/