Mastering DDD Four‑Layer Architecture & Microservice SDKs with D3boot

Microservice SDK under Microservice Architecture

The SDK is similar to a traditional RPC or API package, usually defined as a Maven sub‑module containing Feign interfaces (e.g., service.XxxFeignService), DTOs ( contract.dto.XxxRequest/XxxResponse) and utility classes for data cleaning and simple business logic.

Key design rule: Build the SDK as a large, independent aggregation project, isolating top‑level packages by internal business dimensions rather than a one‑to‑one relationship with a specific business system.

For example, a company may split its top‑level systems into SaaS and PaaS; the PaaS SDK (named PaaSSdk) encapsulates external interfaces such as message center, ChatAI, and app market, allowing SaaS services to depend on a single SDK without pulling in numerous JARs.

DDD Four‑Layer Architecture for Business Projects

The classic DDD four‑layer model serves as the backbone, complemented by other architectural ideas:

Clean Architecture – separates interfaces from implementations across domain and infrastructure layers.

Hexagonal (Diamond) Architecture – centers on domain models and radiates outward.

D3boot Base Framework – provides CRUD interfaces, BOM dependencies, and acts as a glue for quickly building SDKs and business systems.

Layer definitions:

Presentation (Access) Layer: External entry points (controllers) organized by client type (mobile, admin, open).

Application Layer: Cross‑aggregate services, event listeners, and factories.

Domain Layer: Core business rules, rich models, value objects, repository contracts, and domain events; contracts include DTOs, query parameters, and event definitions.

Infrastructure Layer: Technical implementations, repository classes, external service adapters, and other framework‑specific code.

Integrating the D3boot Base Framework

D3boot accelerates the creation of SaaS business systems by providing ready‑made modules for CRUD, multi‑tenant data handling, MQ integration, monitoring, and web utilities.

Key modules include:

base: Core utilities, context objects, common contracts, and conversion tools.

base-data: Rich models, MyBatis‑Plus repositories, tenant isolation support.

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

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

base-monitor: Health checks, version logging, and log‑to‑alert integrations.

base-web: Base CRUD controller, model controller interfaces, global exception handling, Feign fallback, and authentication utilities.

base-bom: Maven BOM for unified dependency version management.

base-contract-parent: Parent POM for quickly scaffolding application SDKs.

base-parent: Parent POM for business projects.

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

The framework is open‑source (see Gitee repository ) and can be customized for specific company needs.