event-processing (local runnable)

Small event-processing microservice core showing:

• EventRouter -> EventHandler
• DependencyClient calls with retry discipline
• Retry only on transient failures
• Exponential backoff + jitter (avoid retry storms)
• Idempotency cache by eventId
• Metrics: events.success, events.failure, per-action metrics

Requirements

• Java 17
• Maven 3.8+

Run tests

mvn test

mvn -q -DskipTests package
java -cp target/event-processing-1.0-SNAPSHOT.jar com.microservice.eventprocessing.App

## Notes
    TransientDependencyException => retryable
    PermanentDependencyException => NOT retryable (fail fast)
    IdempotencyCache prevents duplicate processing by eventId

## Submit event (local)
    curl -X POST http://localhost:8080/events \
    -H "Content-Type: application/json" \
    -d '{"eventId":"evt-1001","type":"PAYMENT","action":"payment.charge","payloadJson":"{\"amount\":25}"}'

## Metrics endpoints
    http://localhost:8080/actuator/health
    http://localhost:8080/actuator/metrics
    http://localhost:8080/actuator/metrics/events.success
    http://localhost:8080/actuator/metrics/events.failure
    http://localhost:8080/actuator/metrics/events.action.success
    http://localhost:8080/actuator/metrics/events.action.failure


What each component is doing (short and practical)

EventController: entry point for local testing (stands in for Kafka consumer).

EventRouter: core orchestration (idempotency → route → retry → metrics).

EventHandler: per-domain logic (PAYMENT/PROFILE) calling dependencies.

DependencyClient: external call boundary (where transient vs permanent errors happen).

RetryPolicy: retries only TransientDependencyException with max attempts + backoff + jitter.

IdempotencyCache: blocks duplicates by eventId (exactly-once behavior at the business level).

MetricsRecorder: records events.success, events.failure, and per-action counters.

## http://localhost:8080/events -> (same eventId) → you’ll get DUPLICATE_IGNORED