REST Controllers in Spring

Complete REST Controller

@RestController
@RequestMapping("/api/v1/products")
@RequiredArgsConstructor
public class ProductController {

    private final ProductService productService;

    @GetMapping
    public ResponseEntity<Page<Product>> getAll(
            @RequestParam(defaultValue = "0") int page,
            @RequestParam(defaultValue = "20") int size) {
        return ResponseEntity.ok(productService.getAll(page, size));
    }

    @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 created = productService.create(request);
        URI location = URI.create("/api/v1/products/" + created.getId());
        return ResponseEntity.created(location).body(created);
    }

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

    @DeleteMapping("/{id}")
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void delete(@PathVariable Long id) {
        productService.delete(id);
    }
}

Request Mapping Annotations

Annotation	HTTP Method	Use Case
@GetMapping	GET	Read resources
@PostMapping	POST	Create resources
@PutMapping	PUT	Full update
@PatchMapping	PATCH	Partial update
@DeleteMapping	DELETE	Delete resources
@RequestMapping	Any	Class-level base path

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 Spring REST Controllers 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