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JavaMail API 基础教程 用于收发文件

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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>消息和标志的删除</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 4 页（共9 页）</nobr></font></td>
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<p>消息的删除涉及使用与消息相关的 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Flags.html">Flags</a></code>（标志）。不同 flag 对应不同的状态，有些由系统定义而有些则由用户定义。下面列出在内部类 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Flags.Flag.html">Flags.Flag</a></code> 中预定义的标志：</p>
<ul>
<li>
<code>Flags.Flag.ANSWERED</code>
</li>
<li>
<code>Flags.Flag.DELETED</code>
</li>
<li>
<code>Flags.Flag.DRAFT</code>
</li>
<li>
<code>Flags.Flag.FLAGGED</code>
</li>
<li>
<code>Flags.Flag.RECENT</code>
</li>
<li>
<code>Flags.Flag.SEEN</code>
</li>
<li>
<code>Flags.Flag.USER</code>
</li>
</ul>
<p>仅仅因为存在一个标志，并不意味着所有邮件服务器或供应商都支持这个标志。例如，除了删除消息标志外，POP 协议不再支持其它任何标志。检查是否存在<i>新</i>邮件，这不是个 POP 任务，而是内建于邮件客户机的任务。为找出哪些标志能被支持，可以用 <code>getPermanentFlags()</code> 向 folder 提出要求。</p>
<p>要删除消息，您可以设置消息的 <code>DELETED</code> flag：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
message.setFlag(Flags.Flag.DELETED, true);
</code>
</pre>
<p>首先，请以 <code>READ_WRITE</code> 模式打开 folder：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
folder.open(Folder.READ_WRITE);
</code>
</pre>
<p>然后，当所有消息的处理完成后，关闭 folder，并传递一个 true 值，从而<i>擦除（expunge）</i>有 delete 标志的消息。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
folder.close(true);
</code>
</pre>
<p>一个 <code>Folder</code> 的 <code>expunge()</code> 方法可以用来删除消息。但 Sun 的 POP3 供应商不支持。其它供应商有的或许能够实现这一功能，而有的则不能。IMAP 供应商极有可能实现此功能。因为 POP 只支持单个对邮箱的访问，对 Sun 的供应商来说，您必需关闭 folder 以删除消息。</p>
<p>要取消标志，只要传递 false 给 <code>setFlag()</code> 方法就行了。想知道是否设置过标志，
可以用 <code>isSet()</code> 检查。</p>
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