DDD分層架構最佳實踐

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"還在單體應用的時候就是分層架構一說，我們用得最多的就是三層架構。而現在已經是微服務時代，在微服務架構模型比較常用的有幾個，例如：整潔架構，CQRS（命令查詢分離）以及六邊形架構。每種架構模型都有自己的應用場景，但其核心都是“","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"高內聚低耦合","attrs":{}},{"type":"text","text":"”原則。而運用","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"領域驅動設計","attrs":{}},{"type":"text","text":"（DDD）理念以應對日常加速的業務變化對架構的影響，架構的邊界越來越清晰，各司其職，這也符合微服務架構的設計思想。以領域驅動設計（DDD）爲理念的分層架構已經成爲微服務架構實踐的最佳實踐方法。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"一、什麼是DDD分層架構","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1. 傳統三層架構","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"要了解DDD分層架構，首先先了解傳統的三層架構。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/58/5892fec13e62ae0a4aabb208c6b7f247.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"傳統三層架構流程：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一步考慮的是數據庫設計，數據表如何建，表之間的關係如何設計","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二步就是搭建數據訪問層，如選一個ORM框架或者拼接SQL操作","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第三步就是業務邏輯的實現，由於我們先設計了數據庫，我們整個的思考都會圍繞着數據庫，想着怎麼寫才能把數據正確地寫入數據庫中，這時CRUD的標準作法就出現了，也就沒有太多考慮面向對象，解耦的事情了，這樣的代碼對日常的維護自然是越來越困難的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第四步表示層主要面向用戶的輸出","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2. DDD分層架構","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c5/c5cd3f68321670cb83242b9ee3a79efd.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"爲了解決高耦合問題並輕鬆應對以後的系統變化，我們提出了運用","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"領域驅動設計","attrs":{}},{"type":"text","text":"的理念來設計架構。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"此段落部分總結來源於歐創新《DDD實踐課》的《07 | DDD分層架構：有效降低層與層之間的依賴》讀後感","attrs":{}}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1）領域層","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先我們拋開數據庫的困擾，","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"先從業務邏輯入手開始","attrs":{}},{"type":"text","text":"，設計時不再考慮數據庫的實現。將以前的業務邏輯層（BLL）拆分成了","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"領域層","attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"應用層","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"領域層聚焦業務對象的業務邏輯實現，體現現實世界業務的邏輯變化。它用來表達業務概念、業務狀態和業務規則，對於業務分析可參照：《使用領域驅動設計分析業務》","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2）應用層","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"應用層是領域層的上層，依賴領域層，是各聚合的協調和編排，原則上是不包括任何業務邏輯。它以較粗粒度的封閉爲前端接口提供支持。除了提供上層調用外，還可以包括事件和消息的訂閱。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3） 用戶接口層","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"用戶接口層面向用戶訪問的數據入向接口，可按不同場景提供不一樣的用戶接口實現。面向Web的可使用http restful的方式提供服務，可增加安全認證、權限校驗，日誌記錄等功能；面向微服務的可使用RPC方式提供服務，可增加限流、熔斷等功能。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"4） 基礎設施層","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"基礎設施層是數據的出向接口，封裝數據調用的技術細節。可爲其它任意層提供服務，但爲了解決耦合的問題採用了依賴倒置原則。其它層只依賴基礎設施的接口，於具體實現進行分離。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"二、DDD分層代碼實現","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1. 結構模型","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bf/bfff156e20d9b904d8fb8ecb2ae26573.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2. 目錄結構","attrs":{}}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":".\n├── pom.xml\n└── src\n ├── main\n │   ├── java\n │   │   └── fun\n │   │   └── barryhome\n │   │   └── ddd\n │   │   ├── WalletApplication.java\n │   │   ├── application\n │   │   │   ├── TradeEventProcessor.java\n │   │   │   ├── TradeMQReceiver.java\n │   │   │   └── TradeManager.java\n │   │   ├── constant\n │   │   │   └── MessageConstant.java\n │   │   ├── controller\n │   │   │   ├── TradeController.java\n │   │   │   ├── WalletController.java\n │   │   │   └── dto\n │   │   │   └── TradeDTO.java\n │   │   ├── domain\n │   │   │   ├── TradeService.java\n │   │   │   ├── TradeServiceImpl.java\n │   │   │   ├── enums\n │   │   │   │   ├── InOutFlag.java\n │   │   │   │   ├── TradeStatus.java\n │   │   │   │   ├── TradeType.java\n │   │   │   │   └── WalletStatus.java\n │   │   │   ├── event\n │   │   │   │   └── TradeEvent.java\n │   │   │   ├── model\n │   │   │   │   ├── BaseEntity.java\n │   │   │   │   ├── TradeRecord.java\n │   │   │   │   └── Wallet.java\n │   │   │   └── repository\n │   │   │   ├── TradeRepository.java\n │   │   │   └── WalletRepository.java\n │   │   └── infrastructure\n │   │   ├── TradeRepositoryImpl.java\n │   │   ├── WalletRepositoryImpl.java\n │   │   ├── cache\n │   │   │   └── Redis.java\n │   │   ├── client\n │   │   │   ├── AuthFeignClient.java\n │   │   │   └── LocalAuthClient.java\n │   │   ├── jpa\n │   │   │   ├── JpaTradeRepository.java\n │   │   │   └── JpaWalletRepository.java\n │   │   └── mq\n │   │   └── RabbitMQSender.java\n │   └── resources\n │   ├── application.properties\n │   └── rabbitmq-spring.xml\n └── test\n └── java\n\n\n\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"此結構爲單一微服務的簡單結構，各層在同一個模塊中。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在大型項目開發過程中，爲了達到核心模塊的權限控制或更好的靈活性可適當調整結構，可參考《 數字錢包系統》系統結構","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3. 領域層實現（domain）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在業務分析（《使用領域驅動設計分析業務》）之後，開始編寫代碼，首先就是寫領域層，創建","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"領域對象","attrs":{}},{"type":"text","text":"和","attrs":{}},{"type":"text","marks":[{"type":"bgcolor","attrs":{"color":"#F6F6F6","name":"user"}}],"text":"領域服務接口","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1）領域對象","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏的領域對象包括實體對象、值對象。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"實體對象","attrs":{}},{"type":"text","text":"：具有唯一標識，能單獨存在且可變化的對象","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"值對象","attrs":{}},{"type":"text","text":"：不能單獨存在或在邏輯層面單獨存在無意義，且不可變化的對象","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"聚合","attrs":{}},{"type":"text","text":"：多個對象的集合，對外是一個整體","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"聚合根","attrs":{}},{"type":"text","text":"：聚合中可代表整個業務操作的實體對象，通過它提供對外訪問操作，它維護聚合內部的數據一致性，它是聚合中對象的管理者","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"代碼示例：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"// 交易\npublic class TradeRecord extends BaseEntity {\n /**\n * 交易號\n */\n @Column(unique = true)\n private String tradeNumber;\n /**\n * 交易金額\n */\n private BigDecimal tradeAmount;\n /**\n * 交易類型\n */\n @Enumerated(EnumType.STRING)\n private TradeType tradeType;\n /**\n * 交易餘額\n */\n private BigDecimal balance;\n /**\n * 錢包\n */\n @ManyToOne\n private Wallet wallet;\n\n /**\n * 交易狀態\n */\n @Enumerated(EnumType.STRING)\n private TradeStatus tradeStatus;\n\n \t@DomainEvents\n public List