### Configure Redis Connection

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Configure your Redis connection details in application.properties or application.yml.

```yaml
spring:
  data:
    redis:
      host: localhost
      port: 6379
```

--------------------------------

### Global Idempotency Configuration

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Configure global default settings for idempotency, including TTL, concurrent strategy, and failure strategy.

```yaml
spring:
  idempotency:
    default-ttl: 24                        # TTL value (default: 24)
    default-time-unit: hours               # TTL unit (default: hours)
    default-on-concurrent: reject          # REJECT or WAIT (default: reject)
    default-on-failure: fail-open          # FAIL_OPEN or FAIL_CLOSED (default: fail-open)
    key-prefix: "idempotency:"             # Redis key prefix (default: "idempotency:")
    lock-timeout: 30s                      # Distributed lock TTL (default: 30s)
    wait-timeout: 10s                      # Max wait time for WAIT strategy (default: 10s)
    wait-poll-initial-interval: 100ms      # Initial poll interval (default: 100ms)
    wait-poll-max-interval: 1s             # Max poll interval after backoff (default: 1s)
```

--------------------------------

### Add Dependency (Gradle Kotlin)

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Add the spring-idempotency-kit dependency to your build.gradle.kts file.

```kotlin
dependencies {
    implementation("io.github.atlancia-labs:spring-idempotency-kit:0.1.0")
}
```

--------------------------------

### Register Custom IdempotencyStorage Bean

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Implement the IdempotencyStorage interface and register it as a Spring bean to use a custom storage backend. The auto-configuration will automatically back off.

```java
@Bean
public IdempotencyStorage customStorage() {
    return new MyIdempotencyStorage();
}
```

--------------------------------

### Concurrent Request Handling with WAIT Strategy

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Configure a method to use the WAIT strategy for concurrent requests, causing subsequent requests to poll until the first completes.

```java
@Idempotent(headerName = "Idempotency-Key", onConcurrent = ConcurrentStrategy.WAIT)
public Response slowOperation(Request request) {
    // second concurrent request will wait for this to finish
}
```

--------------------------------

### Idempotent Method with Header Key

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Annotate a method with @Idempotent to ensure it executes only once per unique key extracted from an HTTP header.

```java
@Idempotent(headerName = "Idempotency-Key")
public OrderResponse createOrder(OrderRequest request) {
    // executed once per unique Idempotency-Key header value
}
```

--------------------------------

### Idempotent Method with SpEL Key

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Annotate a method with @Idempotent to ensure it executes only once per unique key extracted using SpEL expressions from method arguments.

```java
@Idempotent(key = "#request.id")
public PaymentResponse processPayment(PaymentRequest request) {
    // executed once per unique request.id
}
```

--------------------------------

### IdempotencyStorage Interface Definition

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

The core interface for idempotency storage. Implementations must handle atomic operations, lock expiry, and token-aware release.

```java
public interface IdempotencyStorage {
    Optional<IdempotencyResult> get(String key);
    String acquireLock(String key, Duration lockTtl);  // returns lock token, or null if already held
    void store(String key, IdempotencyResult result, Duration ttl);
    void releaseLock(String key, String lockToken);     // token-aware release
    default long keyCount() { return -1; }             // override to enable idempotency.keys.count gauge
}
```

--------------------------------

### Per-Method Failure Strategy Override

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Override the default failure strategy for a specific method using the onFailure attribute in the @Idempotent annotation.

```java
@Idempotent(key = "#id", onFailure = FailureStrategy.FAIL_CLOSED)
public Response criticalPayment(String id) { ... }
```

--------------------------------

### Per-Method TTL Override

Source: https://github.com/atlancia-labs/spring-idempotency-kit/blob/main/Readme.md

Override the default TTL for a specific method using the ttl and timeUnit attributes in the @Idempotent annotation.

```java
@Idempotent(key = "#id", ttl = 1, timeUnit = TimeUnit.MINUTES)
public Response shortLivedOperation(String id) { ... }
```

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