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Real code from lesson guides solving high-concurrency enterprise problems
Guarantees exactly-once processing for high-frequency financial webhooks using atomic setnx tokens.
@Transactional
public PaymentResponse processPayment(String idempotencyKey, PaymentRequest req) {
Boolean acquired = redisTemplate.opsForValue()
.setIfAbsent("lock:idem:" + idempotencyKey, "PROCESSING", Duration.ofSeconds(120));
if (Boolean.FALSE.equals(acquired)) {
throw new DuplicateTransactionException("Request in-flight or already settled: " + idempotencyKey);
}
PaymentRecord record = paymentRepository.save(new PaymentRecord(req));
kafkaProducer.publish("payments.settled", record.toEvent());
return PaymentResponse.from(record);
}