架構必備的領域邊界劃分方法：職責驅動設計

{"type":"doc","content":[{"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","text":"寫該文章的目的是對過去一段時間自我學習知識的總結，通過對職責驅動設計（RDD）的學習發現通過該模式進行對領域職責進行劃分能夠得出很清晰的職責，能有效減少無結論的掰扯，後面部分也有些在實際中的運用，期望能和大家交流起來～"}]}]},{"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"}],"text":"軟件在本質上是複雜的"},{"type":"text","text":"，軟件本身的複雜性在於除了要解決問題域，還要解決非功能性需求和軟件域特有問題：安全性、可用性、可維護性、可擴展性、性能、一致性、容錯性、穩定性、可重用性、冪等、兼容等等，軟件開發者的任務就是製造“簡單”的假象。如何組織複雜的系統？把複雜的事物分解到不同的層次中，層次代表了不同級別的抽象，一層構建於另一層之上，每一層都對上層屏蔽內部複雜度。"}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1.爲什麼使用RDD？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在RDD中，我們認爲“軟件對象具有職責”，這個定義很符合人在社會羣體中分工協作的方式，軟件也是人編寫的，所以根據職責思考設計的軟件系統符合人的行爲習慣，同時更易於理解和管理。在微服務架構中不同系統由不同的組織和人負責，把系統當作對象（人），系統提供的接口就是對象（人）的職責。"}]},{"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":"underline"}],"text":"職責驅動設計的核心是考慮怎樣給對象分配職責，其適用於大到系統、小到對象等任何規模的軟件。職責分配的本質是分工，勞動分工是勞動生產率提高的主要原因"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}},{"type":"strong"}],"text":"："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}},{"type":"strong"}],"text":" 1. 熟練度的提高，專注於某個領域（降低複雜度）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}},{"type":"strong"}],"text":" 2. 時間的節約，同一個人在不同工作來回切換需要耗費大量時間"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}},{"type":"strong"}],"text":" 3. 人工發明的機器和應用（特定領域的工具）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2.如何給對象(元素)分配職責？"}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"color","attrs":{"color":"#FFA940","name":"user"}},{"type":"strong"}],"text":"分配職責應當從清晰的描述職責開始"},{"type":"text","text":"，對於軟件領域對象來說，"},{"type":"text","marks":[{"type":"underline"}],"text":"領域模型"},{"type":"text","text":"描述了領域對象的屬性和關聯，對應類的屬性和引用，"},{"type":"text","marks":[{"type":"underline"}],"text":"用例模型"},{"type":"text","text":"包含一系列的行爲活動，對應類的方法。領域模型創建方式參考："}]},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"學習《UML和模式應用》、UDD、DDD"}]}]}]}]},{"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"}],"text":"使用GRASP模式分配職責"},{"type":"text","text":"，GRASP是通用職責分配模式（General Responsibility Assignment Software Patterns），是對一些基本的職責分配原則進行了命名和描述，共9種模式。"}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}},{"type":"strong"}],"text":"一些GRASP原則是對其他原則和設計模式的歸納，設計模式有上百種，只是記住GoF 23種設計模式就已經很困難了更別提還要記住每種模式的細節，因此需要對設計模式進行有效的歸類，GRASP中的原則描述了模式的本質，除了有助加速設計模式學習之外，對發現現有設計存在的問題也更有效，這就是歸納的價值"}]}]},{"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":"當談論"},{"type":"text","marks":[{"type":"strong"}],"text":"低耦合、高內聚"},{"type":"text","text":"時，我們具體是在談什麼？問題不在於耦合度高、內聚性低，而是在於其產生的負面影響，負面影響往往是在發生"},{"type":"text","marks":[{"type":"strong"}],"text":"變化"},{"type":"text","text":"時體現出來的，這些負面影響會影響到我們開發的效率、穩定性、可維護性、可擴展性、可複用性等等，整個GRASP的核心是如何"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#050505","name":"user"}},{"type":"strong"}],"text":"防止變異"},{"type":"text","text":"（變化）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c8/c84098bf0f4de993cb12adf3ba900a45.png","alt":null,"title":"在學習過程中發現GRASP缺少結構化的展示歸納結果，通過我自己的理解把開發中常用的GoF設計模式、面向對象設計原則、架構設計原則和GRASP進行關聯。注：這個圖可能總結的還不夠準確，正在逐步學習修改。","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3.GRASP職責分配模式"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}}],"text":"3.1 防止變異"}]},{"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":"該模式基本等同於信息隱藏和開閉原則。如何做到在不修改原來功能的前提下對變化的部分進行擴展？識別不穩定因素是特別困難的，也決定了我們能否做出符合開閉原則的設計。"}]},{"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":"strong"}],"text":"問題"},{"type":"text","text":"：如何設計對象、子系統和系統，使其內部的變化或不穩定性不會對其他元素產生不良影響。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"解決方案"},{"type":"text","text":"：識別預計變化或不穩定之處，分配職責用以在這些變化之外創建穩定接口。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"相關原則和模式"},{"type":"text","text":"："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"GRASP：間接性、多態"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"GoF：大量模式"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其他：接口、數據封裝"}]}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}}],"text":"3.2 低耦合、高內聚"}]},{"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":"underline"}],"text":"耦合是對某元素與其他元素之間的連接、感知和依賴程度的度量，內聚是對元素職責的相關性和集中度的度量（"},{"type":"text","text":"這裏的元素指類、系統、子系統等等），耦合和內聚是從不同角度看待問題，他們互相依賴的互相影響的：（以下兩點也可以反過來說）"}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"內聚過低，相關功能分散在不同模塊中，需要增加額外的耦合使這些功能聚合在一起，發生變更時影響多個模塊。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"內聚過高，不相關的功能聚集在一個模塊中，耦合度高，發生變更時會產生意想不到的影響。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2e/2e17eed54adf4a89b608e84e7d688c32.png","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}}],"text":"3.2.1 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或 領域層，如果真的這樣寫就會出現循環依賴問題，通過"},{"type":"text","marks":[{"type":"strong"}],"text":"依賴倒置"},{"type":"text","text":"可以解決依賴問題。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"4.2 六(多)邊形架構（洋蔥圈架構）"}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"六邊形架構(Hexagonal Architecture)，又稱爲"},{"type":"text","marks":[{"type":"strong"}],"text":"端口和適配器"},{"type":"text","text":"架構風格，其中的“六”具體數字沒有特殊的含義，僅僅表示一個“量級”的意思，六邊形的定義只是方便更加形象的理解。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ed/edbc06ddccf596a0cf3dd56503b96fe2.png","alt":null,"title":"六邊形架構","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"六邊形架構提倡用一種新的視角來看待整個系統，該架構中存在兩個區域：“外部區域”和“內部區域”。在外部區域中不同的客戶均可以提交輸入（網絡請求、定時腳本、消息消費等），而內部區域則是處理具體邏輯的地方。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f4/f46cc8b9907e74b55838a8551890711f.png","alt":null,"title":"圖片來源：https://www.jianshu.com/p/d3e8b9ac097b","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"5.案例"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"案例1：Jpa替換爲Mybatis"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@Component\npublic class CloseOrderService {\n @Autowired(required = false)\n @Qualifier(\"rstOrderTransactionManager\")\n JpaTransactionManager tm;\n \n public void invalid_order(Long orderId, Long userId, Short processGroup)\n throws UserException, SystemException, UnknownException {\n //其他邏輯。。。省略\n \n // 開啓事務\n DefaultTransactionDefinition def = new DefaultTransactionDefinition();\n TransactionStatus ts = tm.getTransaction(def);\n\n try {\n order = orderDAO.get(orderId);\n order.setStatusCode(toStatus);\n order.setUpdatedAt(new Timestamp(System.currentTimeMillis()));\n orderDAO.save(order);\n //提交事務\n tm.commit(ts);\n } catch (Exception e) {\n if (!ts.isCompleted()) {\n //回滾\n tm.rollback(ts);\n }\n if (e instanceof SatisfiedStateException) {\n return;\n }\n throw e;\n }\n }\n @Transactional(transactionManager = \"rstOrderTransactionManager\", rollbackFor = Exception.class)\n public void invalidOrder(){\n }\n}\n\n@Component\npublic interface OrderDAO extends JpaRepository {\n @Query(value = \"sql語句\", nativeQuery = true)\n Long generateGlobalOrderId(@Param(\"userId\") Long userId, \n @Param(\"restaurantId\") Long restaurantId, \n @Param(\"seqName\") String seqName);\n}"}]},{"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":"變化帶來的影響："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"如果不出意外對Jpa的使用方式不會產生變更，意味着其相對穩定"},{"type":"text","text":"，所以在當前階段來看以上耦合是正常的也不會產生負面影響。但是在以下場景會讓我們對高耦合有很明顯的體感：大家覺得Jpa不好用，想替換爲Mybatis該怎麼做？代碼中直接使用了繼承JpaRepository的OrderDAO做數據操作，由於Jpa和Mybatis的寫法不同，所以需要把使用到OrderDAO的地方都做替換："}]},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"調用OrderDAO的類（70多個類）都需要替換爲新的dao"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"使用JpaTransactionManager.getTransaction()的位置需要替換爲MyBatis的TransactionManager"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"使用@Transactional(transactionManager = \"rstOrderTransactionManager\")的位置需要改爲編寫事務提交和回滾的代碼塊兒，便於做灰度"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"以上改動的位置需要增加開關做灰度"}]}]}]},{"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"}],"text":"結論："},{"type":"text","text":"由於變更涉及到70多個類，同時事務管理器獲取方式也需要修改，其帶來的影響還是挺大的，不滿足“低耦合”原則，可以使用“多態”原則重新設計。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"案例2：訂單對應的支付單應該由誰來創建？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"拿餓了麼交易系統舉例，當前創建支付單的職責是由bos服務承擔（面向app的一個後端服務）的，接下我們進行分析。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ce/ce0d287f9a174cf29c365dd01fea61e6.png","alt":null,"title":"流程圖","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"支付單創建分爲兩種場景："}]},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"創建訂單和支付單是在一次操作中完成"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"用戶回到訂單列表頁點擊“去支付”時創建支付單"}]}]}]},{"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":"支付單創建依賴："}]},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"訂單號"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"支付金額"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"支付類型"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"一堆支付系統分配的用於識別業務的參數"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2a/2a7e81ecc9869ab856c58e0bfc31f943.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"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":"strong"}],"text":"注1"},{"type":"text","text":"：如果餓了麼只會有外賣一種交易業務，當前的設計還是很穩定的，不會出現太大變化。所以識別變化點才能更好的評判當前系統設計是否合理，如：餓了麼將升級爲本地生活服務公司，根據公司戰略多少能看出我們將來不只外賣業務存在，還會有很多和本地生活相關的交易業務，這些業務會有自己的展示層（app、h5、web）同時對應會有類似bos的服務，如果有10個業務方，在支付場景就需要去對接10次，而由order做就只需要一次（支付作爲工具已經比較穩定，不會有太大變化）。"}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"bos比order多出識別訂單結構的成本。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"bos比order多出認知交易域業務知識的成本。需要深入瞭解交易狀態，這樣才知道什麼狀態才能去支付（一般是去問order服務的開發），打破了邊界。"}]}]}]}]},{"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"}],"text":"結論"},{"type":"text","text":"：bos服務不應該承擔創建支付單的職責，由order承擔最合適。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}