Guangfei.Zhao
1e0cbb86a2
- Introduced integration layer design with Resilience4j for external vendor calls. - Established API design standards with unified response structures and global exception handling. - Defined configuration and service governance using Kubernetes native solutions. - Implemented observability practices including trace ID propagation and structured logging. - Outlined build and multi-environment deployment strategies using Gradle and GitLab CI/CD. - Specified testing strategies across different layers, utilizing JUnit, MockK, Testcontainers, and WireMock.
148 lines
7.3 KiB
Markdown
148 lines
7.3 KiB
Markdown
# 02. 分层规范（后端）
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## 决策
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每个 `domains/*` 模块内部采用简化分层，`domain` 层**可选**，判断标准与 Flutter 端 [02-layering.md](../02-layering.md) 保持一致的思路：
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```
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domains/xxx/
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src/main/kotlin/com/continental/retailapp/xxx/
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api/ # Controller、请求/响应 DTO
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application/ # Service，编排用例、跨 repository 协调
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domain/ # 可选：领域模型、repository/client 接口、状态机/复杂业务规则
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infrastructure/ # JPA repository 实现、外部 client 实现
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```
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## 各层职责
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- **api**：`Controller`（只做参数校验 + 调用 `application`）、请求/响应 DTO。不写业务逻辑，不直接依赖 `infrastructure` 的具体实现类。
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- **application**：`Service`，编排用例、事务边界（`@Transactional` 一般加在这一层）。依赖 `domain` 定义的接口（有 domain 层时），或直接依赖 `infrastructure` 暴露的接口（跳过 domain 层时）。
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- **domain**（可选）：领域模型（可以是纯 Kotlin data class，不一定是 JPA entity）、repository/client 接口、封装多步骤业务规则或状态机的领域服务。不依赖 Spring Web/JPA 相关类型，可以脱离容器单独做单元测试。
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- **infrastructure**：`domain`（或 `application`，跳过 domain 层时）里接口的具体实现——JPA repository 实现、`WebClient`/Feign 外部调用实现。
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## 何时可以跳过 domain 层
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- **可以跳过**：简单 CRUD、没有跨 repository 协调、没有状态机——`application` 直接依赖 `infrastructure` 里定义的 repository/client 接口即可（接口和实现放在同一层）。
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- **必须要有**：多步骤业务规则（如 WebView 换票的状态校验）、需要协调多个数据源（如 `workbench` 聚合多个 Mini 域）、包含状态机或需要独立于容器做单元测试的核心业务逻辑——接口定义在 `domain`，`infrastructure` 反向实现。
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## 依赖方向
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```
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api → application → domain（或直接 → infrastructure 的接口，若跳过 domain）
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domain → 不依赖 api / infrastructure
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infrastructure → 依赖 domain 的接口（若有），依赖 platform-persistence / platform-integration
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```
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`domain` 层的类不 import `org.springframework.web.*` / `jakarta.persistence.*`，保证这一层的单元测试不需要起 Spring 容器、不需要真实数据库。
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## 示例一：有 domain 层（`webview-ticket`，换票——多步骤状态校验）
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```kotlin
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// domain/model/WebviewTicket.kt
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data class WebviewTicket(
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val ticketId: String,
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val storeId: Long,
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val userId: Long,
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val status: TicketStatus,
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val expiresAt: Instant,
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)
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enum class TicketStatus { ISSUED, CONSUMED, EXPIRED, INVALIDATED }
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// domain/repository/WebviewTicketRepository.kt
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interface WebviewTicketRepository {
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fun findActiveTicket(userId: Long, storeId: Long): WebviewTicket?
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fun save(ticket: WebviewTicket)
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}
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// domain/service/IssueWebviewTicketService.kt
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class IssueWebviewTicketService(
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private val ticketRepository: WebviewTicketRepository,
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private val clock: Clock,
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) {
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fun issue(userId: Long, storeId: Long): WebviewTicket {
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val existing = ticketRepository.findActiveTicket(userId, storeId)
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if (existing != null && existing.status == TicketStatus.ISSUED && existing.expiresAt.isAfter(clock.instant())) {
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return existing // 已有有效票据，直接复用，不重复签发
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}
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val ticket = WebviewTicket(
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ticketId = UUID.randomUUID().toString(),
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storeId = storeId,
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userId = userId,
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status = TicketStatus.ISSUED,
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expiresAt = clock.instant().plus(Duration.ofMinutes(5)),
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)
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ticketRepository.save(ticket)
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return ticket
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}
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}
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// application/WebviewTicketAppService.kt
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@Service
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class WebviewTicketAppService(
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private val issueWebviewTicketService: IssueWebviewTicketService,
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) {
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@Transactional
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fun issueTicket(userId: Long, storeId: Long): WebviewTicketResponse {
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val ticket = issueWebviewTicketService.issue(userId, storeId)
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return WebviewTicketResponse(ticket.ticketId, ticket.expiresAt)
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}
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}
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// infrastructure/persistence/WebviewTicketRepositoryImpl.kt
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@Repository
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class WebviewTicketRepositoryImpl(
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private val jpaRepository: WebviewTicketJpaRepository,
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) : WebviewTicketRepository {
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override fun findActiveTicket(userId: Long, storeId: Long): WebviewTicket? =
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jpaRepository.findByUserIdAndStoreIdAndStatus(userId, storeId, TicketStatus.ISSUED)?.toDomain()
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override fun save(ticket: WebviewTicket) {
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jpaRepository.save(ticket.toEntity())
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}
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}
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```
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`IssueWebviewTicketService` 的复用/过期判断规则可以直接用一个假的 `WebviewTicketRepository` 实现做单元测试，不需要起 Spring 容器或真实数据库，也不需要 mock HTTP。
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## 示例二：跳过 domain 层（`identity-store`，门店列表——简单查询）
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```kotlin
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// infrastructure/persistence/StoreRepository.kt
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interface StoreRepository {
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fun findStoresByUserId(userId: Long): List<StoreEntity>
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}
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@Repository
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interface StoreJpaRepository : JpaRepository<StoreEntity, Long>, StoreRepository {
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@Query("select s from StoreEntity s join UserStoreEntity us on us.storeId = s.id where us.userId = :userId")
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override fun findStoresByUserId(userId: Long): List<StoreEntity>
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}
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// application/StoreAppService.kt
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@Service
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class StoreAppService(
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private val storeRepository: StoreRepository,
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) {
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fun listStores(userId: Long): List<StoreResponse> =
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storeRepository.findStoresByUserId(userId).map { StoreResponse(it.id, it.name) }
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}
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```
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没有多步骤规则、没有跨 repository 协调，接口和实现直接放在 `infrastructure`，`application` 直接依赖 `StoreRepository` 这个接口，省掉一层 `domain` 目录。
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## 附录：为什么要分层，以及依赖倒置在这里怎么体现
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如果 `Controller` 里直接写 `EntityManager` 查询、直接 `new WebClient.create(...)` 调用 F6——短期能跑，但会导致：
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1. **业务规则没法脱离容器单独测试**：想验证"换票是否要判断过期时间"，得连 Spring 容器、连数据库一起跑测试。
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2. **换底层实现要动到业务代码**：比如把 JPA 换成 jOOQ，或者把 F6 调用从 `RestTemplate` 换成 `WebClient`，如果业务代码直接依赖具体实现类，改动会散落得到处都是。
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分层的关键不是"分了几层"，而是**依赖方向单向流动**，`domain` 只定义接口（"我需要一个能查到 `WebviewTicket` 的东西"），不关心 `infrastructure` 具体怎么实现——这是[依赖倒置原则](https://en.wikipedia.org/wiki/Dependency_inversion_principle)。我们只取这套思想里最实用的一层隔离，不套用完整的 DDD 战术模式（聚合根、值对象、领域事件那一整套），避免简单模块也被迫按重量级模板写代码。
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## 参考链接
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- [依赖倒置原则（Dependency Inversion Principle）](https://en.wikipedia.org/wiki/Dependency_inversion_principle)
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- [The Clean Architecture（Uncle Bob 原文）](https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html)
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- [Spring 官方分层架构指南](https://docs.spring.io/spring-framework/reference/core/beans/introduction.html)
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