JavaMail从字符串发送邮件附件 - 编码UTF-8

Question

我的应用程序必须发送一个文本文件,它首先必须生成一个String.该文本包含非ASCII符号,所以我希望它是UTF-8.我已经尝试了很多变种,但我收到的所有附件都是一些问号.并且,当我发送与邮件正文相同的文本时,它可以正常工作.

以下是生成带附件的MimeBodyPart的代码行:

String attachment = "??????";
messageBodyPart.setContent(new String(attachment.getBytes("UTF-8"),
    "UTF-8"),"text/plain; charset=UTF-8");

我也尝试使用没有任何转换的字符串,只使用字节,现在,如你所见,我试图从字节生成一个字符串...

我究竟做错了什么？(我确实记得在另一个项目中这样做,但是我不再能够访问它的源代码).

先感谢您.提莫菲.

UPDATE

阅读完回复后,经过一些不成功的试验后,我认为最好发布我的邮件代码.我有一个Mailer类,它负责邮件发送,其他类可以调用它的静态sendMessage()方法来发送消息.这一切都在Google App Engine上运行.

public static void sendMessage(String to, String subject, String msgBody,
            String attachment) throws AddressException, MessagingException {

    Properties props = new Properties();

    Session mailSession = Session.getDefaultInstance(props, null);
    Message msg = new MimeMessage(mailSession);
    String email = "bla-bla-bla"; // userService.getCurrentUser().getEmail();

    msg.setFrom(new InternetAddress(email));
    msg.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

    InternetAddress[] addresses = { new InternetAddress("bla-bla-bla") };

    msg.setReplyTo(addresses);
    msg.setSubject(subject);

    Calendar cal = Calendar.getInstance();

    String fileName = cal.get(Calendar.YEAR) + "_"
            + cal.get(Calendar.MONTH) + "_"
            + cal.get(Calendar.DAY_OF_MONTH) + "_"
            + cal.get(Calendar.HOUR_OF_DAY) + "_"
            + cal.get(Calendar.MINUTE) + "_" + cal.get(Calendar.SECOND)
            + "_" + cal.get(Calendar.MILLISECOND) + ".txt";

    // create the message part
    MimeBodyPart messageBodyPart = new MimeBodyPart();

    // fill message
    // Here we should have the msgBody.
    // Sending attachment contents for debugging only.
    messageBodyPart.setText(attachment + " - 4", "UTF-8", "plain");

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

    MimeBodyPart att = new MimeBodyPart();
    att.setText(attachment, "UTF-8", "plain");
    att.addHeader("Content-Type", "text/plain; charset=UTF-8"); 

    att.setFileName(fileName);
    multipart.addBodyPart(att);

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

    Transport.send(msg);
}

在另一个类中调用此东西的行是:

Mailer.sendMessage("mymail@example.com", "Test", "No body", "??????, ? ????? ??????");

奇怪的是,邮件的原始来源是(忽略看似无关的标题):

Message-ID: <00163662e7107ccbe3049c1402fb@google.com>
Date: Sat, 12 Feb 2011 11:21:01 +0000
Subject: Pages
From: mymail@example.com
To: mymail@example.com
Content-Type: multipart/mixed; boundary=00163662e7107ccbd4049c1402fa

--00163662e7107ccbd4049c1402fa
Content-Type: text/plain; charset=KOI8-R; format=flowed; delsp=yes
Content-Transfer-Encoding: base64

8NLJ18XULCDxIMvV08/LINTFy9PUwSAtIDQNCg==
--00163662e7107ccbd4049c1402fa
Content-Type: text/plain; charset=US-ASCII; name="2011_1_12_11_21_1_691.txt"
Content-Disposition: attachment; filename="2011_1_12_11_21_1_691.txt"
Content-Transfer-Encoding: base64

Pz8/Pz8/LCA/ID8/Pz8/ID8/Pz8/Pw==
--00163662e7107ccbd4049c1402fa--

我只是不明白,为什么charsets与我想要设置的不同,以及它们来自哪里.

Answer 1

将内容类型设置为application/octet-stream:

MimeBodyPart attachmentPart = new MimeBodyPart();

try {
  DataSource ds = new ByteArrayDataSource(attachment.getBytes("UTF-8"), "application/octet-stream");
  attachmentPart = new MimeBodyPart();
  attachmentPart.setDataHandler(new DataHandler(ds));
} 
catch (Exception e) {
  Logger.getLogger("Blina").log(Level.SEVERE, Misc.getStackTrace(e));
}

attachmentPart.setFileName(fileName);
multipart.addBodyPart(attachmentPart);

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

Answer 2

有类似的情况,下面的代码解决了它:

MimeBodyPart att = new MimeBodyPart();
att.setFileName(MimeUtility.encodeText(fileName));

Answer 3

如果问题出在文件名而不是正文中，则以下代码对我的（希伯来语）案例有帮助：

MimeBodyPart attachment = new MimeBodyPart();
attachment.setFileName(MimeUtility.encodeText(filename, "UTF-8", null));