Spring Boot @RestController vs @RequestMapping

🚀 Introduction: Understanding @RestController vs @RequestMapping

In Spring Boot, both @RestController and @RequestMapping are used in RESTful APIs, but they serve different purposes.

✅ Key Differences:

Feature	@RestController	@RequestMapping
Purpose	Marks a class as a REST controller (returns JSON responses).	Maps HTTP requests to controller classes or methods.
Applies To	Class level (on controllers)	Class and method level (for URL mappings)
Implicit Behavior	Includes @ResponseBody by default.	Does not include @ResponseBody (must be explicitly added).
Common Usage	Used for REST APIs (microservices, JSON responses).	Used for defining request mappings in controllers.

1️⃣ Understanding @RestController in Spring Boot

📌 Use @RestController to define RESTful APIs that return JSON responses.

✅ @RestController = @Controller + @ResponseBody

Example: Using @RestController for a REST API

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

    @GetMapping("/{id}")
    public User getUserById(@PathVariable int id) {
        return new User(id, "Ramesh");
    }
}

📌 How It Works:

• The class is marked as a REST API controller.
• The @RestController annotation automatically applies @ResponseBody, so the return value is converted to JSON.

📌 Example API Response (GET /api/users/1):

{
  "id": 1,
  "name": "Ramesh"
}

✅ Ideal for building RESTful services that return JSON responses.

2️⃣ Understanding @RequestMapping in Spring Boot

📌 Use @RequestMapping to define URL mappings for controllers.

✅ It can be applied at class level and method level.
✅ It supports GET, POST, PUT, DELETE, PATCH requests.

Example: Using @RequestMapping at Class and Method Level

@Controller
@RequestMapping("/web")
public class WebController {

    @RequestMapping(value = "/home", method = RequestMethod.GET)
    public String homePage() {
        return "home"; // Returns home.html (Thymeleaf/JSP view)
    }
}

📌 How It Works:

• The @RequestMapping at class level applies to all methods inside it (/web).
• The method maps /web/home to home.html (a view page).
• Unlike @RestController, this method returns a view name, not JSON.

3️⃣ @RequestMapping in a REST API (Without @RestController)

📌 If you use @Controller, you must add @ResponseBody manually to return JSON.

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

    @RequestMapping(value = "/users/{id}", method = RequestMethod.GET)
    @ResponseBody
    public User getUserById(@PathVariable int id) {
        return new User(id, "Ramesh");
    }
}

✅ Adding @ResponseBody ensures JSON output in REST APIs.

📌 Example API Response (GET /api/users/1):

{
  "id": 1,
  "name": "Ramesh"
}

✅ Equivalent to using @RestController, but requires @ResponseBody.

4️⃣ @GetMapping, @PostMapping, @PutMapping, @DeleteMapping vs @RequestMapping

Spring Boot provides shortcut annotations for common HTTP methods:

Annotation	Equivalent @RequestMapping
@GetMapping("/users")	@RequestMapping(value = "/users", method = RequestMethod.GET)
@PostMapping("/users")	@RequestMapping(value = "/users", method = RequestMethod.POST)
@PutMapping("/users/{id}")	@RequestMapping(value = "/users/{id}", method = RequestMethod.PUT)
@DeleteMapping("/users/{id}")	@RequestMapping(value = "/users/{id}", method = RequestMethod.DELETE)

✅ Using @GetMapping, @PostMapping, etc., makes the code cleaner and more readable.

5️⃣ When to Use @RestController vs @RequestMapping?

Use Case	Use @RestController	Use @RequestMapping
RESTful API (returns JSON)	✅ Yes	❌ No (Requires @ResponseBody)
MVC application (returns views)	❌ No	✅ Yes (For rendering HTML views)
Returning JSON responses	✅ Yes (Automatic)	❌ No (Needs @ResponseBody)
HTTP method-specific mappings	✅ Yes (@GetMapping, @PostMapping, etc.)	✅ Yes (@RequestMapping(method = ...))

📌 Best Practice:
✔ Use @RestController for REST APIs (JSON responses).
✔ Use @Controller + @RequestMapping for web applications (Thymeleaf, JSP).

6️⃣ Combining @RestController and @RequestMapping

📌 Example: Using @RestController with @RequestMapping for REST API

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

    @GetMapping("/{id}")
    public User getUserById(@PathVariable int id) {
        return new User(id, "Ramesh");
    }
}

✅ Combining @RestController and @RequestMapping makes REST API development easy.

🎯 Summary: Best Practices for @RestController and @RequestMapping

✅ Use @RestController when building REST APIs that return JSON.
✅ Use @Controller with @RequestMapping when building MVC applications.
✅ Use @GetMapping, @PostMapping, etc., instead of @RequestMapping(method = ...) for cleaner code.
✅ If using @Controller for REST, always add @ResponseBody manually.

🚀 Following these best practices ensures clean, maintainable Spring Boot applications!

📢 Share this guide with developers to help them master @RestController and @RequestMapping in Spring Boot! 🚀