Integrating DDD Four‑Layer Architecture and Microservice SDK with the D3boot Framework

Application SDK under Microservice Architecture

The SDK is essentially an RPC/API module defined as a Maven sub‑module that contains Feign interfaces (e.g., service.XxxFeignService), DTO objects ( contract.dto.XxxRequest / XxxResponse), and utility classes for data cleaning and simple business logic encapsulation.

Key design rule: The SDK should be built as a large‑scale independent aggregate, with top‑level packages isolated by internal business dimensions, rather than a one‑to‑one mapping with a specific business system.

For example, a company may split its top‑level systems into SaaS and PaaS applications; the corresponding PaaSSdk aggregates external interfaces and lightweight business logic for modules such as Message Center, ChatAI, and App Marketplace. SaaS services can simply depend on PaaSSdk without pulling in numerous unrelated JARs.

DDD Four‑Layer Architecture for Business Projects

The classic DDD four‑layer model (Presentation, Application, Domain, Infrastructure) is used for single‑service engineering, while the microservice view integrates multiple such services via the SDK.

Layer definitions:

Access Layer: Exposes system entry points (controllers) and separates APIs by client type (mobile, admin, open).

Application Layer: Orchestrates cross‑aggregate services, domain events, and factories.

Domain Layer: Holds core business rules, rich models, value objects, repository contracts, domain services, and DTO contracts.

Infrastructure Layer: Implements technical concerns (repositories, external service adapters, MQ, etc.).

Integrating the D3boot Base Framework

D3boot is a lightweight microservice foundation that speeds up CRUD development, enforces clean architecture, and supports multi‑tenant SaaS applications. It combines DDD principles with a “fat model” approach for convenient CRUD operations while still allowing “thin model” factories for complex object construction.

The framework is organized into several Maven modules:

base: Core utilities, context holders, common contracts (R, Page, events, exceptions, status codes), and conversion tools.

base-data: Rich models, generic repositories, MyBatis‑Plus integration, and tenant‑aware data handling.

base-mq: Kafka integration with annotation‑driven consumers.

base-kit: General purpose utilities (caching, events, language helpers, threading, web helpers).

base-monitor: Health checks, version logging, and log‑to‑robot alerting.

base-web: Base CRUD controller, model‑specific controllers, global exception handling, Feign fallback, interceptors, and authentication support.

base-bom: Maven Bill‑of‑Materials for unified dependency version management.

base-contract-parent: Parent POM for building application SDKs.

base-parent: Parent POM for building business services.

ddd-demo: Sample project demonstrating the DDD four‑layer style on top of D3boot.

Final Thoughts

The author emphasizes keeping the base framework lightweight, extracting reusable components into separate modules, and open‑sourcing the project for others to customize. The source code is available on Gitee, and detailed usage instructions are provided in the repository's README.

Promotional notes and community links are included at the end of the original article, but the technical content above constitutes the core academic value of the piece.