@RestController
@RequestMapping("/api/payments")
public class PaymentController {

    @PostMapping
    @Idempotent(key = "#request.transactionId", ttl = 24, timeUnit = TimeUnit.HOURS)
    public PaymentResponse processPayment(@RequestBody PaymentRequest request) {
        // This method will be executed only once for each transactionId
        return paymentService.process(request);
    }
}

// Parameter by name
@Idempotent(key = "#transactionId")

// Nested property
@Idempotent(key = "#request.orderId")

// Combined parameters
@Idempotent(key = "#userId + ':' + #orderId")

// Parameter by index
@Idempotent(key = "#p0.id")

@ExceptionHandler(IdempotencyException.class)
public ResponseEntity<ErrorResponse> handleIdempotency(IdempotencyException ex) {
    return ResponseEntity
            .status(HttpStatus.CONFLICT)
            .body(new ErrorResponse(ex.getMessage(), ex.getIdempotencyKey()));
}

@Service
public class PaymentService {

    @Idempotent(key = "#payment.transactionId", ttl = 24, timeUnit = TimeUnit.HOURS)
    public PaymentResult processPayment(Payment payment) {
        // Safe from duplicate processing
        return gateway.charge(payment);
    }
}

@Service
public class NotificationService {

    @Idempotent(key = "#userId + ':' + #eventType", ttl = 5, timeUnit = TimeUnit.MINUTES)
    public void sendNotification(String userId, String eventType, String message) {
        // User will receive only one notification per 5 minutes
        emailService.send(userId, message);
    }
}