Spring Boot web annotations

Spring Boot web annotations

Spring Boot web applications rely heavily on annotations to configure controllers, handle requests, and define responses.
Here’s a breakdown of the most commonly used Spring Web annotations with simple examples:

1. @RestController

  • Combines @Controller and @ResponseBody.
  • Marks a class as a web controller that directly returns data (usually JSON).
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, Spring Boot!";
    }
}

2. @RequestMapping

  • Used at class level and method level to map HTTP requests to handler methods.
import org.springframework.web.bind.annotation.*;

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

    @GetMapping("/{id}")
    public String getUser(@PathVariable int id) {
        return "User with ID: " + id;
    }

    @PostMapping
    public String createUser(@RequestBody String user) {
        return "Created User: " + user;
    }
}

3. @GetMapping, @PostMapping, @PutMapping, @DeleteMapping

  • Specialized versions of @RequestMapping for specific HTTP methods.
@RestController
@RequestMapping("/products")
public class ProductController {

    @GetMapping
    public String getAllProducts() {
        return "List of products";
    }

    @PostMapping
    public String addProduct(@RequestBody String product) {
        return "Added product: " + product;
    }

    @PutMapping("/{id}")
    public String updateProduct(@PathVariable int id, @RequestBody String product) {
        return "Updated product " + id + " with: " + product;
    }

    @DeleteMapping("/{id}")
    public String deleteProduct(@PathVariable int id) {
        return "Deleted product with ID: " + id;
    }
}

4. @PathVariable

  • Extracts values from the URI path.
@GetMapping("/orders/{orderId}")
public String getOrder(@PathVariable int orderId) {
    return "Order ID: " + orderId;
}

5. @RequestParam

  • Extracts values from query parameters.
@GetMapping("/search")
public String search(@RequestParam String keyword) {
    return "Searching for: " + keyword;
}

Example request:

GET /search?keyword=laptop

6. @RequestBody

  • Maps the request body (usually JSON) to a Java object.
@PostMapping("/register")
public String registerUser(@RequestBody User user) {
    return "Registered user: " + user.getName();
}

7. @ResponseBody

  • Used on methods to indicate return value should go directly in the HTTP response (not a view).
    (Since @RestController already applies this, you’ll mostly use it in @Controller classes.)
@Controller
public class MyController {

    @GetMapping("/message")
    @ResponseBody
    public String getMessage() {
        return "Direct Response Body";
    }
}

8. @Controller

  • Marks a class as a Spring MVC Controller (used when rendering views like JSP/Thymeleaf, not just JSON).
@Controller
public class WebController {

    @GetMapping("/home")
    public String homePage() {
        return "home";  // returns "home.html" from templates
    }
}

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