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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>第三步：综合应用 Ant 和 XDoclet 来配置组件</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr> 第 4 页（共14 页）</nobr></font></td>
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<p>您一般<i>不</i>愿把初始化参数硬编码到源代码中。有关使用 <code><init-param></code> 的全部概念是使 Web 组件可被应用程序组装器（application assembler）定制为 J2EE 应用程序。</p>
<p>更好的方法是把初始参数设为指向类似 @bye@ 和 @hi@ 中的标记，然后使用启用了过滤的 Ant 复制来为正确的应用程序传递正确的标记值。这里假定您使用 Ant 来构建项目。</p>
<p>您可以使用 Ant 过滤来把配置文件中的标记替换成它们在部署环境中的正确的值。过滤器是支持配置多个应用程序的 J2EE 组件的另一种方式。以下是根据条件来配置 <i>web.xml</i> 的示例 Ant 脚本：
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
<project name="filtering" default="run">
<target name="spanishSetup" if="spanish">
<filter token="bye" value="adios"/>
<filter token="hi" value="hola"/>
</target>
<target name="englishSetup" unless="spanish">
<filter token="bye" value="goodbye"/>
<filter token="hi" value="hello"/>
</target>
<target name="setup" depends="spanishSetup,englishSetup"/>
<target name="run" depends="setup">
<copy todir="${workspace}/WEB-INF" filtering="true">
<fileset dir="./WEB-INF"/>
</copy>
</target>
</project>
</code>
</pre>
在上面的 Ant 示例中，<code>englishSetup</code> 目标中的过滤器把 bye 标记设为 <i>goodbye</i>，而 <code>spanishSetup</code> 目标中的过滤器把 bye 标记设为 <i>adios</i>。</p>
<p>稍后，当脚本使用启用了过滤的复制任务时，它把过滤器应用于复制任务指定的文件集中的所有的文件。若 <i>spanish</i> 属性被设置，则启用了过滤的复制任务把所有的字符串 @bye@ 替换为 <i>adios</i>，若 <i>spanish</i> 属性没有被设置，则 <i>goodbye</i>。</p>
<p>
<b>更容易的方法……</b>
<br>
虽然这是解决这个问题的一个方法，但是还有更容易的方法。Ant 属性可被用来设置 XDoclet 中的每个属性值。因为您用 XDoclet Ant 任务来生成相关的文件，所以 XDoclet 可访问所有的 ant 属性。因此，您可以这样来设置值：
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
...
* @web.servlet-init-param name="hi"
* value="${basic.servlet.hi}"
*
* @web.servlet-init-param name="bye"
* value="${basic.servlet.bye}"
...
*/
public class BasicServlet extends HttpServlet {
</code>
</pre>
然后，当您生成 <i>web.xml</i> 文件时，<code>hi</code> 和 <code>bye</code> 初始化参数被设置成 Ant 构建脚本中设置的 <code>basic.servlet.hi</code> 和 <code>basic.servlet.bye</code> 属性的当前值。XDoclet 和 Ant 相互配合从而使 J2EE 组件被配置成应用程序。主要的好处是可按每个应用程序来配置组件。想象一下每个应用程序的主构建文件，这个文件调用每个组件的构建文件，把配置某个应用程序的组件所需的信息传递给构建文件。</p>
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