Building Your First REST Controller

Building Your First REST Controller

Controllers are the front door of a Spring web application: they receive HTTP requests, delegate work, and return responses. With @RestController you mark a class as a web controller whose return values are written directly to the HTTP response body, typically as JSON.

Annotations at a glance

@RestController is a convenience that combines @Controller with @ResponseBody. Class-level or method-level mappings attach URLs to handler methods. Common ones are @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping, which match the corresponding HTTP methods.

@RestController
@RequestMapping("/api/products")
public class ProductController {
    private final ProductService service;

    public ProductController(ProductService service) {
        this.service = service;
    }

    @GetMapping
    public List<Product> allProducts() {
        return service.findAll();
    }
}

What makes it RESTful

RESTful design uses resources and HTTP verbs: GET retrieves, POST creates, PUT replaces, DELETE removes. Paths name nouns (like /api/products), not actions. The client and server negotiate with JSON bodies and status codes rather than action URLs.

Return values

Returning a plain object or list lets Jackson convert it to JSON automatically. Returning ResponseEntity gives you control over the HTTP status, headers, and body together, which is handy for created-resource responses and error payloads.

Controllers stay thin

Move business logic into service beans and persistence into repositories. A controller should map requests to service calls and translate results into responses. This keeps each layer focused and testable in isolation.

Key Points

• @RestController writes return values directly to the response body.
• Use @GetMapping, @PostMapping, and friends for HTTP-verb routing.
• Class-level @RequestMapping groups endpoints under a common path.
• Return JSON objects, lists, or ResponseEntity for full control.
• Keep controllers thin and delegate to services.