How is idempotency organized in your system?

Idempotency is a property of an operation where multiple executions produce the same result as a single execution.

In Java applications, idempotency is usually achieved through several methods:

• Using unique request identifiers (idempotency keys). The client generates a unique key for the operation, the server saves the state associated with this key, and for subsequent requests with the same key, it returns the same result without re-executing the operation.

• Designing operations to be idempotent at the business logic level. For example, update operations that set a specific value rather than changing it relative to the current value.

• Using transactions and state checks. Before executing an operation, it checks whether it has already been performed (for example, based on the status in the database).

• Storing the state of operations. Information about completed operations is stored in a database or cache to prevent re-execution.

Example of using an idempotency key in a REST API:

@PostMapping("/payments")
public ResponseEntity<?> createPayment(@RequestHeader("Idempotency-Key") String key, @RequestBody PaymentRequest request) {
    if (paymentService.existsByIdempotencyKey(key)) {
        return ResponseEntity.ok(paymentService.getByIdempotencyKey(key));
    }
    Payment payment = paymentService.processPayment(request);
    paymentService.saveWithIdempotencyKey(payment, key);
    return ResponseEntity.status(HttpStatus.CREATED).body(payment);
}

Thus, a repeated request with the same key will not create a duplicate operation.