{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Salesforce是首批大規模採用OpenJDK 11的大型企業之一，在2018年底OpenJDK 11發佈後不久，Salesforce就開始了OpenJDK 11的採用之旅。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"前沿嗎？ 當然是。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"安全嗎？ 絕對地。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"你可能還不知道，Salesforce在整合前沿、轉型技術，並以安全、可靠、無縫的方式，同時在不損害其"},{"type":"link","attrs":{"href":"https:\/\/www.salesforce.com\/company\/our-story\/","title":null,"type":null},"content":[{"type":"text","text":"#1核心價值：信任"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"的前提下，將這些技術提供給客戶方面一直處於行業的領先地位。從"},{"type":"link","attrs":{"href":"https:\/\/www.cncf.io\/case-studies\/salesforce\/","title":null,"type":null},"content":[{"type":"text","text":"gRPC"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"到"},{"type":"link","attrs":{"href":"https:\/\/engineering.salesforce.com\/adopting-kubernetes-46b6c13b204b","title":null,"type":null},"content":[{"type":"text","text":"Kubernetes"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"，Salesforce在新技術領域有着早期大膽探索的歷史。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在本文的案例中，將主要的Salesforce CRM應用程序升級到OpenJDK 11是一項龐大的跨組織工作。 把它做好，不僅能爲我們帶來幾年的Java運行時創新紅利，也能爲我們的客戶提供更好的體驗，併爲開源社區做出貢獻。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"背景"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"2018年末，OpenJDK 11作爲Java最新的長期支持（LTS）版本面世。這開啓了一個人們期待已久的機遇，推動了Salesforce應用程序的向前發展，併爲我們的內部開發人員帶來了巨大的新特性和創新。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"爲什麼我們認爲我們可以安全地從OpenJDK 8（上一個最新的LTS版本）過渡到OpenJDK 11呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"首先，我們並不是一蹴而就的。對於OpenJDK 9和OpenJDK 10這兩個版本，雖然我們只打算將它們作爲墊腳石，而不在生產環境中使用，但一旦它們的版本可用，我們就會立即升級到對應版本。正如你所料，最困難的部分是從OpenJDK 8升級到OpenJDK 9，這需要對Salesforce應用程序進行重大的更改。從OpenJDK 9升級到OpenJDK 10，再從OpenJDK 10升級到OpenJDK 11，都只需做相對較小的改動。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 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11版本的字符串覆蓋配置屬性一樣簡單。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"也就是說，我們面臨的另一個挑戰是，我們的OpenJDK 11遷移工作跨越了多個版本週期，我們必須確保任何支持OpenJDK 11的增量更改都不會打破我們的生產環境（生產環境仍然是基於OpenJDK 8部署的），也不能對客戶的信任產生任何負面影響。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 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9帶來了一個影響類加載的重大變更。這是對"},{"type":"link","attrs":{"href":"https:\/\/docs.oracle.com\/javase\/8\/docs\/technotes\/guides\/standards\/index.html","title":null,"type":null},"content":[{"type":"text","text":"授權標準覆蓋機制"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"（Endorsed Standards Override Mechanism，用於支持加載包含授權標準和獨立技術實現的JAR文件）和"},{"type":"link","attrs":{"href":"https:\/\/docs.oracle.com\/javase\/8\/docs\/technotes\/guides\/extensions\/index.html","title":null,"type":null},"content":[{"type":"text","text":"擴展機制"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"（ Extension Mechanism，用於支持加載包含擴展或可選軟件包的JAR文件）的移除。由於Salesforce應用程序過去依賴於這兩種機制，因此必須使用 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標誌的組合，將所有受影響的JAR文件遷移到Salesforce應用程序的模塊路徑下。不過，這些非模塊化的JAR文件都無需轉換爲模塊：它們作爲依賴項被放置在Salesforce應用程序的模塊路徑上，從而自動成爲模塊化的。此功能被稱爲自動模塊化，創建它是爲了減輕將現有應用程序轉換爲新模塊系統的負擔。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"影響Salesforce應用程序的另一個變更是刪除了Salesforce應用程序所依賴的Java Enterprise Edition（“Java EE”）API。Java 9開始將這些API分離到它們各自的模塊中，這些模塊被註解爲不推薦使用，以便刪除，這表明了在將來的版本中會刪除它們的意圖。這些模塊包含在運行時鏡像中，但默認情況下未啓用。因而，它們必須通過 "},{"type":"codeinline","content":[{"type":"text","text":"--add modules"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 標識顯式“激活”。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"從Java11開始，這些模塊不再包含在運行時中（"},{"type":"link","attrs":{"href":"https:\/\/openjdk.java.net\/jeps\/320","title":null,"type":null},"content":[{"type":"text","text":"參見JEP 320：刪除Java EE和CORBA模塊"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"）。相反，Java EE和CORBA技術的獨立版本作爲Maven構件發佈，並可以從第三方網站（如Maven Central）上獲取，我們從那裏下載了它們並將它們添加到了Salesforce應用程序的模塊路徑中。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"向後不兼容"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在將Salesforce應用程序的Java運行時遷移到OpenJDK 11時，我們發現了許多向後不兼容的變更。其中大多數都是“設計使然”，並且是涵蓋在版本說明中了的，正如下面所要討論的那樣。(有一個true的迴歸影響了布爾型bean屬性的內省；這是由OpenJDK實現本身的一個bug引起的，我們報告了這個bug，並且它已經被修復了。）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"設計上向後不兼容變更的例子很明顯，因爲它會導致JVM在啓動時中斷，並出現如下的錯誤："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"Unrecognized VM option '
Salesforce在生產中大規模採用OpenJDK 11的一年
{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Salesforce是首批大規模採用OpenJDK 11的大型企業之一，在2018年底OpenJDK 11發佈後不久，Salesforce就開始了OpenJDK 11的採用之旅。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"前沿嗎？ 當然是。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 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"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"你可能還不知道，Salesforce在整合前沿、轉型技術，並以安全、可靠、無縫的方式，同時在不損害其"},{"type":"link","attrs":{"href":"https:\/\/www.salesforce.com\/company\/our-story\/","title":null,"type":null},"content":[{"type":"text","text":"#1核心價值：信任"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"的前提下，將這些技術提供給客戶方面一直處於行業的領先地位。從"},{"type":"link","attrs":{"href":"https:\/\/www.cncf.io\/case-studies\/salesforce\/","title":null,"type":null},"content":[{"type":"text","text":"gRPC"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"到"},{"type":"link","attrs":{"href":"https:\/\/engineering.salesforce.com\/adopting-kubernetes-46b6c13b204b","title":null,"type":null},"content":[{"type":"text","text":"Kubernetes"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"，Salesforce在新技術領域有着早期大膽探索的歷史。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在本文的案例中，將主要的Salesforce CRM應用程序升級到OpenJDK 11是一項龐大的跨組織工作。 把它做好，不僅能爲我們帶來幾年的Java運行時創新紅利，也能爲我們的客戶提供更好的體驗，併爲開源社區做出貢獻。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"背景"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"2018年末，OpenJDK 11作爲Java最新的長期支持（LTS）版本面世。這開啓了一個人們期待已久的機遇，推動了Salesforce應用程序的向前發展，併爲我們的內部開發人員帶來了巨大的新特性和創新。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"爲什麼我們認爲我們可以安全地從OpenJDK 8（上一個最新的LTS版本）過渡到OpenJDK 11呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"首先，我們並不是一蹴而就的。對於OpenJDK 9和OpenJDK 10這兩個版本，雖然我們只打算將它們作爲墊腳石，而不在生產環境中使用，但一旦它們的版本可用，我們就會立即升級到對應版本。正如你所料，最困難的部分是從OpenJDK 8升級到OpenJDK 9，這需要對Salesforce應用程序進行重大的更改。從OpenJDK 9升級到OpenJDK 10，再從OpenJDK 10升級到OpenJDK 11，都只需做相對較小的改動。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"另外，Java的向後兼容性保證允許用舊版本Java開發編譯的應用程序代碼能運行在新的版本上，這一功能的威力不容小覷。向後兼容性爲遷移提供了巨大的幫助，這樣我們的大多數代碼都不需要更改。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Salesforce應用程序利用Java向後兼容性的方法之一是，將用於構建Salesforce應用程序的Java版本與用於啓動它的Java版本分開。這使我們能夠首先集中精力將過程的一端從OpenJDK 8升級到OpenJDK 11，而另一端仍保持在OpenJDK 8上不變，並將其升級到OpenJDK 11的時間往後推遲。我們內部開發人員的目標是，通過在初始化和啓動Salesforce應用程序的腳本中隱藏所有的差異和複雜性的方式，讓OpenJDK 8和OpenJDK 11運行時之間的切換儘可能的簡單和無縫。因此，對於我們的開發人員來說，升級到OpenJDK 11運行時就像用OpenJDK 11版本的字符串覆蓋配置屬性一樣簡單。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"也就是說，我們面臨的另一個挑戰是，我們的OpenJDK 11遷移工作跨越了多個版本週期，我們必須確保任何支持OpenJDK 11的增量更改都不會打破我們的生產環境（生產環境仍然是基於OpenJDK 8部署的），也不能對客戶的信任產生任何負面影響。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"平臺的變更&挑戰"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"當我們一個接一個地升級OpenJDK版本時，我們遇到了Java平臺的許多顯著變更。而我們的遷移之路漫長且需有條不紊地推進，這意味着這些變更會給我們帶來了很多挑戰，但在這裏我們只討論其中的幾個。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"類路徑與模塊化"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https:\/\/en.wikipedia.org\/wiki\/Java_version_history#Java_SE_9","title":null,"type":null},"content":[{"type":"text","text":"Java SE 9"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"平臺引入的重大變更之一就是Java平臺模塊系統（Java Platform Module System，JPMS）。JPMS將JDK劃分爲多個模塊，每個模塊都是一組命名唯一且可重用的相關包。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"好消息是，Java 9仍然支持傳統的類路徑，它能與模塊路徑一起工作，並映射到一個被稱爲未命名模塊的特殊模塊上。因此，構成Salesforce應用程序類路徑的所有JAR文件都會自動加入模塊系統，從而導致了傳統類路徑和模塊路徑的混合。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"實際上，Salesforce應用程序的整個類加載器層次結構都保留在Java 9及更高版本中。它由我們的Web服務器和Servlet容器錨定，委託給OSGi類加載器，而OSGi類加載器又委託給Java運行時的內置類加載器。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"然而，作爲Jigsaw計劃的一部分，Java 9帶來了一個影響類加載的重大變更。這是對"},{"type":"link","attrs":{"href":"https:\/\/docs.oracle.com\/javase\/8\/docs\/technotes\/guides\/standards\/index.html","title":null,"type":null},"content":[{"type":"text","text":"授權標準覆蓋機制"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"（Endorsed Standards Override Mechanism，用於支持加載包含授權標準和獨立技術實現的JAR文件）和"},{"type":"link","attrs":{"href":"https:\/\/docs.oracle.com\/javase\/8\/docs\/technotes\/guides\/extensions\/index.html","title":null,"type":null},"content":[{"type":"text","text":"擴展機制"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"（ Extension Mechanism，用於支持加載包含擴展或可選軟件包的JAR文件）的移除。由於Salesforce應用程序過去依賴於這兩種機制，因此必須使用 "},{"type":"codeinline","content":[{"type":"text","text":"-module-path"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 、 "},{"type":"codeinline","content":[{"type":"text","text":"-upgrade-module-path"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 和 "},{"type":"codeinline","content":[{"type":"text","text":"-patch-module"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 標誌的組合，將所有受影響的JAR文件遷移到Salesforce應用程序的模塊路徑下。不過，這些非模塊化的JAR文件都無需轉換爲模塊：它們作爲依賴項被放置在Salesforce應用程序的模塊路徑上，從而自動成爲模塊化的。此功能被稱爲自動模塊化，創建它是爲了減輕將現有應用程序轉換爲新模塊系統的負擔。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"影響Salesforce應用程序的另一個變更是刪除了Salesforce應用程序所依賴的Java Enterprise Edition（“Java EE”）API。Java 9開始將這些API分離到它們各自的模塊中，這些模塊被註解爲不推薦使用，以便刪除，這表明了在將來的版本中會刪除它們的意圖。這些模塊包含在運行時鏡像中，但默認情況下未啓用。因而，它們必須通過 "},{"type":"codeinline","content":[{"type":"text","text":"--add modules"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 標識顯式“激活”。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"從Java11開始，這些模塊不再包含在運行時中（"},{"type":"link","attrs":{"href":"https:\/\/openjdk.java.net\/jeps\/320","title":null,"type":null},"content":[{"type":"text","text":"參見JEP 320：刪除Java EE和CORBA模塊"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"）。相反，Java EE和CORBA技術的獨立版本作爲Maven構件發佈，並可以從第三方網站（如Maven Central）上獲取，我們從那裏下載了它們並將它們添加到了Salesforce應用程序的模塊路徑中。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"向後不兼容"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在將Salesforce應用程序的Java運行時遷移到OpenJDK 11時，我們發現了許多向後不兼容的變更。其中大多數都是“設計使然”，並且是涵蓋在版本說明中了的，正如下面所要討論的那樣。(有一個true的迴歸影響了布爾型bean屬性的內省；這是由OpenJDK實現本身的一個bug引起的，我們報告了這個bug，並且它已經被修復了。）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"設計上向後不兼容變更的例子很明顯，因爲它會導致JVM在啓動時中斷，並出現如下的錯誤："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"Unrecognized VM option '
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