What is idempotency and how can it be ensured?

Idempotency is a property of an operation where multiple executions with the same input produce the same result as a single execution. In the context of web services, this means that repeated calls to the same request do not further change the system's state.

To ensure idempotency, you can:

• Use unique request identifiers (e.g., UUIDs) and store them so that repeated requests with the same ID do not lead to repeated changes.
• Design operations so that repeated execution does not alter the state (e.g., setting a value rather than incrementing).
• Use methods in REST API that are inherently idempotent (GET, PUT, DELETE).

An example in Java: when creating an order, you can generate a unique clientRequestId and check whether such a request has already been processed to avoid creating duplicates.