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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>開發流</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 3 頁（共15 頁）</nobr></font></td>
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<p>左圖顯示了用 JDO 進行開發的過程。當采用 JDO 環境時，您需要利用決策點和迭代來改進此過程。</p>
<p>第一步是構建源代碼（.java 文件）。理論上，我們在這一步構建的對象源不必具有持久性。例如您可以構建一組代表人員（PersonImpl.java）、地址（AddressImpl.java）以及部門（DepartmentImpl.java）的源文件而不需要知道這些類最終將與數據庫進行相互操作。使用標準 Java 編譯器，將這些源文件編譯成 .class 文件。實際上，如果知道我們要將 JDO 用于對象持久性，能使我們將更好的性能技術構建到對象模型中。</p>
<p>下一步是確定什么類需要持久性。確定類之后，上一步中生成的 .class 文件輸出就用<i>類增強器</i>增強。這一步很可能由開發實現類的人員來完成，因為他或她具有關于實現的基本知識。為了使用類增強器，您必須構建元數據文件（以 XML 格式），該文件標識哪些類需要持久性，以及有關這些類的任何附加信息。類增強器將 .class 文件與元數據組合在一起。輸出是修改過的 .class 文件。</p>
<p>類增強使構建過程與現有 IDE 集成很困難。它也是用 JDO 進行開發的最有爭議的方面。修改 .class 文件是一種需好好研究的巧妙形式，而且已開發了工具來協助直接進行類的修改。盡管如此，要讓您理解涉及創建與源代碼并不對應的 .class 文件的過程，仍很困難。如果您使用諸如 Ant 那樣的構建工具，那么它會在幕后為您無縫地完成一切操作。</p>
<p>下一步是使用已增強的 .class 文件和 JDO 接口來構建應用程序對象。盡管持久性對象不使用 JDO API 和實現，但應用程序對象將使用 JDO API 來控制持久對象的持久性、事務以及查詢機制。在應用程序中，要與之打交道的主要部分是與特定數據源相關聯的 <code>PersistenceManager</code>。我們將在整篇教程中都使用持久性管理器。</p>
<p>在構建應用程序時，我們還使用實際的數據庫模式。通常，JDO 實現包含一個工具，它從前幾步中創建的元數據和已增強的類文件中自動創建數據庫模式。</p>
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