Difference Between @Controller and @RestController in Spring Boot

 🚀 Introduction: Understanding @Controller vs @RestController

Spring Boot provides two main annotations for handling web requests:

• @Controller (Used for traditional MVC applications with views).
• @RestController (Used for REST APIs returning JSON/XML responses).

✅ Key Differences:

1️⃣ Understanding @Controller in Spring Boot

📌 Use @Controller when building traditional web applications that return HTML views.

1. Example: Using @Controller for an MVC Web Application

@Controller
public class HomeController {

    @GetMapping("/")
    public String home(Model model) {
        model.addAttribute("message", "Welcome to Spring Boot!");
        return "home"; // Returns home.html (Thymeleaf/JSP/Freemarker)
    }
}

📌 How It Works:

• The method returns a view name (home) instead of JSON.
• Spring Boot resolves it to a template (home.html).
• The Model object carries data to the view.

2️⃣ Understanding @RestController in Spring Boot

📌 Use @RestController when building RESTful APIs that return JSON responses.

1. Example: Using @RestController for a REST API

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping("/users")
    public List<String> getUsers() {
        return List.of("Ramesh", "Suresh", "Mahesh");
    }
}

📌 How It Works:

• The method returns JSON directly (["Ramesh", "Suresh", "Mahesh"]).
• No need for @ResponseBody—Spring Boot automatically converts the return object to JSON.

3️⃣ How @RestController Internally Uses @ResponseBody

📌 @RestController = @Controller + @ResponseBody

Example: Using @Controller with @ResponseBody (Equivalent to @RestController)

@Controller
@RequestMapping("/api")
public class UserController {

    @GetMapping("/users")
    @ResponseBody // Manually specifying response type
    public List<String> getUsers() {
        return List.of("Ramesh", "Suresh", "Mahesh");
    }
}

✅ In @RestController, @ResponseBody is applied automatically, so you don’t need to add it manually.

4️⃣ Returning HTTP Responses in @RestController

📌 Use ResponseEntity<> in @RestController to customize HTTP responses.

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping("/user/{id}")
    public ResponseEntity<String> getUser(@PathVariable int id) {
        if (id == 1) {
            return ResponseEntity.ok("User: Ramesh");
        } else {
            return ResponseEntity.status(HttpStatus.NOT_FOUND)
                    .body("User not found");
        }
    }
}

📌 How It Works:
 ✅ Returns 200 OK when the user exists.
 ✅ Returns 404 Not Found when the user does not exist.

5️⃣ When to Use @Controller vs @RestController?

When to Use @Controller vs @RestController?

🎯 Summary: Best Practices for @Controller and @RestController

✅ Use @Controller for MVC applications that return views (Thymeleaf, JSP).
 ✅ Use @RestController for REST APIs that return JSON responses.
 ✅ Use @ResponseBody if you need JSON responses inside @Controller.
 ✅ Use ResponseEntity<> in @RestController to customize HTTP responses.
 ✅ Follow REST API best practices for building scalable microservices.

🚀 Following these best practices ensures a clean and maintainable Spring Boot application!

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