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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>展望 JDO 的未来</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 1 页（共4 页）</nobr></font></td>
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<p>JDO 是极佳的第一版规范，并且作为对象持久性机制，它填补了一个空白。另一方面，JDO 在该领域中极具竞争力。五年前 SanFrancisco 应用程序组件框架（SanFrancisco Application Component Framework）是用对象持久性层构建的（尽管 SanFrancisco Classic 已不再可用）；EJB 技术是实体 bean 和 CMP 的基础；另外，XML 数据绑定和 Java 序列化当然也都是强有力的竞争者。这些机制都对对象持久性提供了自己绝妙的解决方案，但没有一个机制真正适合面向对象的编程范例。最后，JDBC 通常在持久性方面胜出，因为它很显然是关系型，就如通常存储在数据库中的数据。</p>
<p>JDO 将证明自己是解决目前面向对象程序员一直头疼的许多难题的一种有效机制，但它不能解决所有问题。使用 JDO 会使我们的编程方式发生细微的变化，诸如强制执行对象所有权规则、添加指针从所包含的对象指向对象所有者，以及进行其它更改以提高对象映射的性能和导航性。从应用程序方面而言，我们必须确保没有把对象留在数据库中，还要确保使用了能为特定用户界面获得最佳性能的 JDO 选项。</p>
<p>如果有这样那样的缺点，我还是会选择 JDO。该技术与实体 bean 一样重要，而且它还要轻量级得多。实体 bean 的一个轻量级替代方案是 EJB 程序员一直强烈要求得到的技术，集成 JDO 和 EJB 的机制可以实现这一方案（虽然详细讨论超出了本教程范围）。可能这其中很重要的事实是，对面向对象程序员而言，JDO 比 JDBC 更自然，而且它比 Java 序列化或 XML 数据绑定更适合于企业。</p>
<p>不管 JDO 是否准备用于产品级应用程序开发，它都值得考虑。完成本教程后，下次对对象范例评估持久性机制时，希望您把它作为一个选项。</p>
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