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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Message</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 3 頁（共8 頁）</nobr></font></td>
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<p>一旦獲得 <code>Session</code> 對象，就可以繼續創建要發送的消息。這由 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Message.html">Message</a></code> 類來完成。因為 <code>Message</code> 是個抽象類，您必需用一個子類，多數情況下為 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/internet/MimeMessage.html">javax.mail.internet.MimeMessage</a></code>。<code>MimeMessage</code> 是個能理解 MIME 類型和頭的電子郵件消息，正如不同 RFC 中所定義的。雖然在某些頭部域非 ASCII 字符也能被譯碼，但 Message 頭只能被限制為用 US-ASCII 字符。</p>
<p>要創建一個 <code>Message</code>，請將 <code>Session</code> 對象傳遞給 <code>MimeMessage</code> 構造器：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
MimeMessage message = new MimeMessage(session);
</code>
</pre>
<p>注意：還存在其它構造器，如用按 RFC822 格式的輸入流來創建消息。</p>
<p>一旦獲得消息，您就可以設置各個部分，因為 <code>Message</code> 實現 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/Part.html">Part</a> </code> 接口（且 <code>MimeMessage</code> 實現 <code><a href="http://java.sun.com/products/javamail/javadocs/javax/mail/internet/MimePart.html">MimePart</a> </code>）。設置內容的基本機制是 <code>setContent()</code> 方法，同時使用參數，分別代表內容和 mime 類型：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
message.setContent("Hello", "text/plain");
</code>
</pre>
<p>但如果，您知道您在使用 <code>MimeMessage</code>，而且消息是純文本格式，您就可以用 <code>setText()</code> 方法，它只需要代表實際內容的參數，（ MIME 類型缺省為 text/plain）：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
message.setText("Hello");
</code>
</pre>
<p>后一種格式是設置純文本消息內容的首選機制。至于發送其它類型的消息，如 HTML 文件格式的消息，我們首選前者。</p>
<p>用 <code>setSubject()</code> 方法設置 subject（主題）：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
message.setSubject("First");
</code>
</pre>
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