ADR 0002: Use Spring Events for Internal Communication

Status

Accepted

Context

Orders should trigger payment behavior, but the orders module should not depend on payment implementation details. Introducing Kafka or RabbitMQ would make the project look distributed without a real need.

Decision

Orders publish OrderPlacedEvent through the shared EventPublisher port. ecommerce-app adapts that port to Spring’s in-process event publisher. Payment listens with a transactional event listener after commit.

Consequences

Benefits:

• order placement remains decoupled from payment
• event flow is testable without external infrastructure
• payment is not triggered for rolled-back orders

Trade-offs:

• events are in-process and not durable
• failures in payment handling need explicit retry or outbox support later
• event contracts still create a compile-time dependency from payment to orders