u/Entire-Position9690

Spring Idempotency Kit is a production-ready library that ensures methods execute exactly once per unique key — preventing duplicate operations in distributed systems.

Problem it solves: Retries, timeouts, and concurrent requests cause duplicate executions. Double charges, repeated orders, webhook duplication. This library eliminates that.

All you do:

@Idempotent(headerName = "Idempotency-Key")
public PaymentResponse processPayment(PaymentRequest request) {
    // Same key = same result, every time
}

The library handles:

• Redis-backed caching — first request executes, retries return cached result
• Distributed locking — concurrent duplicates are rejected or wait for the original to finish
• Failure strategies — fail-open (keep running) or fail-closed (503 if Redis is down)
• Built-in metrics — cache hits, conflicts, execution timing
• Zero boilerplate — Spring Boot auto-configuration, just annotate

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How It Works

1. Client sends a unique key (header or derived from request)
2. Cache hit → return immediately
3. Cache miss → acquire distributed lock, execute, store result
4. Retry with same key → returns cached result

Requirements

• Java 21+
• Spring Boot 3.4+
• Redis

Links

• GitHub
• Maven Central

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