ddd4j Architecture

Overview

ddd4j's stable center is the framework-agnostic domain, CQRS, and SPI layer. The outer modules deliver data, messaging, web, authentication, caching, observability, and runtime adapters.

When to Use

• Deciding which module should own a new capability, port, or adapter.
• Reviewing dependency direction — whether the domain layer imports framework types.
• Tracing a core port (CommandBus, Publisher, SubjectProvider, Repository) to its actual registered adapter.
• Deciding whether a new broker, ORM client, or HTTP integration belongs in core or in a capability module.
• Reviewing how Spring, Guice, and Quarkus CDI share the same core contracts.
• Landing a new capability: where it goes, what registers it, and what proves it works.

When NOT to Use

Do not use this skill when: