j-javamail-6-8.html

javamail1.3的详细API说明

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<a name="navskip"></a><td height="25" colspan="4"><img alt="6.JavaMail API 的使用" src="imagemaster/titlebar6.jpg" border="0" height="25" width="562"></td>
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>附件的处理</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 8 页（共9 页）</nobr></font></td>
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<font size="2" face="Verdana, Arial, Helvetica">
<p>附件是邮件消息的相关资源，如通常不包含在消息正文里文本文件、电子表格或图像等。常见的邮件程序，如 Eudora 和 pine 之类，可以用 JavaMail API 将资源 <i>attach（附加）</i> 到您的消息上，就可以在收到消息时得到。</p>
<p>
<b>附件的发送：</b>
<br>
发送附件非常像转发消息。您建立各部分以组成完整消息。完成第一部件，即消息正文后，您添加其它部件，其中每个 <code>DataHandler</code> 都代表附件，而不是转发消息情况下的共享处理程序。如果从文件中读附件，附件的数据源是 <code> <a href="http://java.sun.com/products/javabeans/glasgow/javadocs/javax/activation/FileDataSource.html">FileDataSource</a></code>。而如果从 URL 中读时，附件的数据源是 <code> <a href="http://java.sun.com/products/javabeans/glasgow/javadocs/javax/activation/URLDataSource.html">URLDataSource</a></code>。一旦存在 <code>DataSource</code>，只要先把它传递给 <code><a href="http://java.sun.com/products/javabeans/glasgow/javadocs/javax/activation/DataHandler.html">DataHandler</a></code> 构造器，最后再用 <code>setDataHandler()</code> 把它附加到 <code>BodyPart</code>。假定您要保留附件的原始文件名，最终要做的是用 <code>BodyPart</code> 的 <code>setFileName()</code> 方法设置与附件相关的文件名。如下所示：</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  // Define message
  Message message = new MimeMessage(session);
  message.setFrom(new InternetAddress(from));
  message.addRecipient(Message.RecipientType.TO,
    new InternetAddress(to));
  message.setSubject("Hello JavaMail Attachment");

  // Create the message part
  BodyPart messageBodyPart = new MimeBodyPart();

  // Fill the message
  messageBodyPart.setText("Pardon Ideas");

  Multipart multipart = new MimeMultipart();
  multipart.addBodyPart(messageBodyPart);

  // Part two is attachment
  messageBodyPart = new MimeBodyPart();
  DataSource source = new FileDataSource(filename);
  messageBodyPart.setDataHandler(new DataHandler(source));
  messageBodyPart.setFileName(filename);
  multipart.addBodyPart(messageBodyPart);

  // Put parts in message
  message.setContent(multipart);

  // Send the message
  Transport.send(message);
  </code>
</pre>
<p>就消息引入附件时，若程序是个 servlet （小服务程序），除告知消息发送到何处外，还必需上载附件。可以将 <code>multipart/form-data</code> 表单编码类型（form encoding type）用于每个上载文件的处理。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
&lt;FORM ENCTYPE="multipart/form-data"
    method=post action="/myservlet"&gt;
  &lt;INPUT TYPE="file" NAME="thefile"&gt;
  &lt;INPUT TYPE="submit" VALUE="Upload"&gt;
&lt;/FORM&gt;
</code>
</pre>
<p>注意：消息大小由 SMTP 服务器而不是 JavaMail API 来限制。如果您碰到问题，可以考虑用设置 ms 和 mx 参数的方法增大 Java 堆大小。</p>
<p>
<b>练习：</b>
<br>

<a href="j-javamail-8-10.html">练习 5. 如何发送附件</a>
</p>
<p>
<b>附件的获取：</b>
<br>
从消息中获取附件比发送它们棘手些，因为 MIME 没有简单的关于附件的概念。当消息包含附件时，消息的内容是个 <code>Multipart</code> 对象。接着，您需要处理每个 <code>Part</code>，获取主要内容和附件。标有从 <code>part.getDisposition()</code> 获得的 <code>Part.ATTACHMENT</code> 配置（disposition）的部件（Part）无疑就是附件。但是，没有配置（以及一个非文本 MIME 类型）和带  <code>Part.INLINE</code> 配置的部件也可能是附件。当配置要么是 <code>Part.ATTACHMENT</code>，要么是 <code>Part.INLINE</code> 时，这个消息部件的内容就能被保存。只要用 <code>getFileName()</code> 和
<code>getInputStream()</code> 就能分别得到原始文件名和输入流。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
Multipart mp = (Multipart)message.getContent();

for (int i=0, n=multipart.getCount(); i&lt;n; i++) {
  Part part = multipart.getBodyPart(i));

  String disposition = part.getDisposition();

  if ((disposition != null) &amp;&amp;
       ((disposition.equals(Part.ATTACHMENT) ||
          (disposition.equals(Part.INLINE))) {
    saveFile(part.getFileName(), part.getInputStream());
  }
}
</code>
</pre>
<p>
<code>saveFile()</code> 方法仅依据文件名创建了一个 <code>File</code>，它从输入流中将字节读出，然后写入到文件中。万一文件已经存在，就在文件名后添加一个数字作为新文件名，如果这个文件名仍存在，则继续添，直到找不到这样的文件名为止。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
// from saveFile()
File file = new File(filename);
for (int i=0; file.exists(); i++) {
  file = new File(filename+i);
}
</code>
</pre>
<p>上面的代码涵盖了最简单的情况 — 消息中各部件恰当的标记了。要涵盖所有情况，还要在配置为空时进行处理，并且获取部件的 MIME 类型来进行相应处理。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
if (disposition == null) {
  // Check if plain
  MimeBodyPart mbp = (MimeBodyPart)part;
  if (mbp.isMimeType("text/plain")) {
     // Handle plain
  } else {
     // Special non-attachment cases here of image/gif, text/html, ...
  }
  ...
}
</code>
</pre>
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