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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>消息和標志的刪除</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 4 頁（共9 頁）</nobr></font></td>
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<p>消息的刪除涉及使用與消息相關的 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Flags.html">Flags</a></code>（標志）。不同 flag 對應不同的狀態，有些由系統定義而有些則由用戶定義。下面列出在內部類 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Flags.Flag.html">Flags.Flag</a></code> 中預定義的標志：</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>僅僅因為存在一個標志，并不意味著所有郵件服務器或供應商都支持這個標志。例如，除了刪除消息標志外，POP 協議不再支持其它任何標志。檢查是否存在<i>新</i>郵件，這不是個 POP 任務，而是內建于郵件客戶機的任務。為找出哪些標志能被支持，可以用 <code>getPermanentFlags()</code> 向 folder 提出要求。</p>
<p>要刪除消息，您可以設置消息的 <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，請以 <code>READ_WRITE</code> 模式打開 folder：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
folder.open(Folder.READ_WRITE);
</code>
</pre>
<p>然后，當所有消息的處理完成后，關閉 folder，并傳遞一個 true 值，從而<i>擦除（expunge）</i>有 delete 標志的消息。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
folder.close(true);
</code>
</pre>
<p>一個 <code>Folder</code> 的 <code>expunge()</code> 方法可以用來刪除消息。但 Sun 的 POP3 供應商不支持。其它供應商有的或許能夠實現這一功能，而有的則不能。IMAP 供應商極有可能實現此功能。因為 POP 只支持單個對郵箱的訪問，對 Sun 的供應商來說，您必需關閉 folder 以刪除消息。</p>
<p>要取消標志，只要傳遞 false 給 <code>setFlag()</code> 方法就行了。想知道是否設置過標志，
可以用 <code>isSet()</code> 檢查。</p>
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