@RestController :

This annotation in the Spring Framework is used to create RESTful web services in Java. It's applied to a class to indicate that the class will handle incoming HTTP requests and produce responses suitable for RESTful APIs.


Here's a brief breakdown:

Purpose: @RestController combines the functionality of @Controller (for handling requests) and @ResponseBody (for converting method return values to response data). It's specifically designed for building APIs that follow the REST architectural style.

Usage: Annotate a class with @RestController. Inside this class, you define methods to handle various HTTP requests (e.g., GET, POST) by annotating these methods with HTTP-specific annotations like @GetMapping, @PostMapping, etc.

Response Format: When a method in a @RestController class is called, its return value is automatically converted to a format suitable for the response. This is often JSON or XML, depending on the client's request and server configuration.

Example:

import org.springframework.web.bind.annotation.GetMapping; 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController; 
@RestController 
@RequestMapping("/api")

public class UserController { 
@GetMapping("/users") 
public List<User> getUsers() {
// In a real application, you would fetch users from a database or another source
        List<User> users = userService.getAllUsers(); 
return users;
 }
    
    // Other methods for creating, updating, deleting users, etc.
}

@RestController: This annotation is applied to the class UserController, indicating that it will handle HTTP requests for a RESTful service.

@RequestMapping("/api"): This annotation is used at the class level to specify the base URL path for all endpoints defined within the class. In this case, all endpoints within this controller will have URLs starting with "/api".

@GetMapping("/users"): This annotation is applied to the getUsers() method to handle HTTP GET requests with the path "/api/users". This method returns a list of User objects, which will be automatically converted to JSON (or XML, if configured) and sent as the response.

userService.getAllUsers(): This is a hypothetical method call. In a real application, you would likely inject a service layer that interacts with a database or some other data source to retrieve the list of users.

Conclusion:

Overall, the @RestController annotation simplifies the process of creating RESTful services in Spring by combining the functionality of @Controller (which handles general MVC requests) and @ResponseBody (which indicates that the method's return value should be included in the response body). This helps you focus on defining your API's endpoints and logic while letting Spring handle the conversion of data to the appropriate format for the response.