### Build and Verify Project

Source: https://github.com/josipmusa/idempotency4j/blob/main/CONTRIBUTING.md

Run this command to compile, test, and check formatting for a clean build. It's the baseline for any contribution.

```bash
mvn verify
```

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

### Add Spring Boot Starter Dependency

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Include the idempotency-spring-boot-starter and a storage backend dependency in your Maven project. Replace VERSION with the latest version.

```xml
<dependency>
    <groupId>io.github.josipmusa</groupId>
    <artifactId>idempotency-spring-boot-starter</artifactId>
    <version>VERSION</version>
</dependency>

<!-- Pick one storage backend -->
<dependency>
    <groupId>io.github.josipmusa</groupId>
    <artifactId>idempotency-jdbc</artifactId>
    <version>VERSION</version>
</dependency>
```

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

### Run All Tests

Source: https://github.com/josipmusa/idempotency4j/blob/main/CONTRIBUTING.md

Execute all unit and integration tests for the project. Ensure Docker is running if testing provider modules that use Testcontainers.

```bash
mvn test
```

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

### Apply Code Formatting

Source: https://github.com/josipmusa/idempotency4j/blob/main/CONTRIBUTING.md

Automatically fix any code formatting violations enforced by Spotless and Palantir Java Format before committing.

```bash
mvn spotless:apply
```

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

### Test Specific Module

Source: https://github.com/josipmusa/idempotency4j/blob/main/CONTRIBUTING.md

Use these commands to test a specific module and its upstream dependencies without running the full test suite. Ensure SNAPSHOT versions resolve correctly.

```bash
mvn test -pl idempotency-core -am
```

```bash
mvn test -pl providers/idempotency-jdbc -am
```

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

### Use BOM for Dependency Management

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Utilize the idempotency-bom to manage versions of all idempotency modules in your Maven project.

```xml
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>io.github.josipmusa</groupId>
            <artifactId>idempotency-bom</artifactId>
            <version>VERSION</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
```

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

### Client Request with Idempotency-Key Header

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Clients must include a client-generated Idempotency-Key in the request header for idempotency to be enforced. The key should be a UUID.

```http
POST /payments
Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000
Content-Type: application/json

{ "amount": 100, "currency": "USD" }
```

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

### Idempotency Configuration Properties

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Configure Idempotency4j globally using YAML properties. These settings can be overridden by per-endpoint annotation values.

```yaml
idempotency:
  key-header: Idempotency-Key     # Header name carrying the key. Default: Idempotency-Key
  default-ttl: PT24H              # Default TTL for stored responses. Default: 24h
  default-lock-timeout: PT10S     # Default lock timeout. Default: 10s
  max-body-bytes: 1048576         # Max request body size to fingerprint in bytes. Default: 1 MiB
  filter-order: 0                 # Order of the idempotency filter in the filter chain. Default: 0
  purge:
    enabled: true                 # Whether to register the purge scheduler. Default: true
    cron: "0 0 * * * *"          # Cron expression for purging expired records. Default: hourly
```

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

### Idempotent Annotation Configuration

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Configure the `@Idempotent` annotation with TTL, lock timeout, and requirement settings. TTL and lock timeout use ISO-8601 duration format.

```java
@Idempotent(
    ttl = "PT24H",          // How long to keep the stored response (ISO-8601). Default: 24h
    lockTimeout = "PT10S",  // How long a concurrent duplicate waits. Default: 10s
    required = true         // Whether a missing key header is an error. Default: true
)
```

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

### Register Custom ResponseSanitizer Bean

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Register a ResponseSanitizer bean to strip or redact sensitive fields from HTTP response bodies before they are stored for idempotency. The default implementation does nothing.

```java
import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpHeaders;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

// Assuming StoredResponse and ResponseSanitizer are defined elsewhere
// import com.example.idempotency.StoredResponse;
// import com.example.idempotency.ResponseSanitizer;

public class IdempotencyConfig {

    @Bean
    public ResponseSanitizer responseSanitizer() {
        return response -> {
            // Remove sensitive headers, redact body, etc.
            Map<String, List<String>> headers = new HashMap<>(response.headers());
            headers.remove("Set-Cookie");
            return new StoredResponse(response.statusCode(), headers, response.body(), response.completedAt());
        };
    }
}
```

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

### Annotate Endpoints for Idempotency

Source: https://github.com/josipmusa/idempotency4j/blob/main/README.md

Apply the @Idempotent annotation to Spring controller methods that require idempotency. This ensures that requests with the same Idempotency-Key are processed only once.

```java
@PostMapping("/payments")
@Idempotent
public ResponseEntity<Payment> createPayment(@RequestBody PaymentRequest request) {
    // Runs exactly once per unique Idempotency-Key value.
    // Subsequent identical requests get the stored response replayed.
    return ResponseEntity.ok(paymentService.charge(request));
}
```

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