@RestController

@RestController — REST API

@RestController
@RequestMapping("/api/products")
@Tag(name = "Products", description = "Product management")
public class ProductController {

    private final ProductService productService;

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

    @GetMapping
    public ResponseEntity<List<Product>> getAll() {
        return ResponseEntity.ok(productService.getAll());
    }

    @GetMapping("/{id}")
    public ResponseEntity<Product> getById(@PathVariable Long id) {
        return productService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }

    @PostMapping
    public ResponseEntity<Product> create(
            @Valid @RequestBody CreateProductRequest request) {
        Product product = productService.create(request);
        return ResponseEntity.status(201).body(product);
    }

    @PutMapping("/{id}")
    public ResponseEntity<Product> update(
            @PathVariable Long id,
            @Valid @RequestBody UpdateProductRequest request) {
        return ResponseEntity.ok(productService.update(id, request));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> delete(@PathVariable Long id) {
        productService.delete(id);
        return ResponseEntity.noContent().build();
    }
}

ResponseEntity Usage

Method	Status	Use Case
ResponseEntity.ok()	200	Successful GET/PUT/PATCH
ResponseEntity.status(201)	201	Successful POST
ResponseEntity.noContent()	204	Successful DELETE
ResponseEntity.notFound()	404	Resource not found
ResponseEntity.badRequest()	400	Invalid input

Principles

• Stateless communication
• Client-server separation
• Cacheable responses
• Uniform interface

HTTP Methods

• GET: Read (idempotent, safe)
• POST: Create
• PUT: Full update (idempotent)
• PATCH: Partial update
• DELETE: Remove (idempotent)

Status Codes

• 2xx: Success
• 3xx: Redirection
• 4xx: Client error
• 5xx: Server error

Key Points

• Understanding @RestController Annotation is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes