Java Mail 不支持电子邮件主题中的 UTF-8 字符

Question

这是我设置邮件主题的代码:

  String bodyMessage="Dear Renavçilçleç Françoisç InCites™";
  String subject = "Your new InCites™ subscription";

  Properties _sessionProperties = new Properties();
  _sessionProperties.put("mail.transport.protocol", "smtp");
  _sessionProperties.put("mail.smtp.host", "hostname");
  _sessionProperties.put("mail.smtp.port", "25");

  Session session = Session.getInstance(_sessionProperties, null);

  MimeMessage mimemsg = new MimeMessage(session);
  mimemsg.addRecipients(Message.RecipientType.TO, "xxx@gmail.com");
  mimemsg.setSubject(subject, "UTF-8");

  // Create a multi-part message
  MimeMultipart multipart = new MimeMultipart();
  // Set the subType
  multipart.setSubType("alternative");
  BodyPart part = new MimeBodyPart();

  part.setContent(bodyMessage, "charset=UTF-8");

  // Set the emailBody and emailType to MIME BodyPart
  part.setDataHandler(new DataHandler(new ByteArrayDataSource(
      bodyMessage, "text/html;")));

  // Add the MIME BodyPart to MIME multiPart
  multipart.addBodyPart(part);

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

  // Send message
  Transport.send(mimemsg);

但在电子邮件主题中它仍然显示为 “您的新 InCites™ 订阅”

Answer 1

你在这里提到的主题完全由ASCII字符组成。这包括有趣的特殊字符 ™。如果您希望它是 Unicode，只需使用 Unicode 而不是 HTML 转义。邮件与 HTML 无关。

mimemsg.setSubject("Your new InCites\u2122 subscription", "UTF-8");

这应该将主题编码为类似于 =?UTF-8?Q?Your...subscription?= 的形式，如 RFC 2047 中指定的那样.

完整示例代码:

package so4406538;

import java.io.IOException;
import java.util.Properties;

import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.MimeMessage;

public class MailDemo {

  public static void main(String[] args) throws MessagingException, IOException {
    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props);
    MimeMessage message = new MimeMessage(session);
    message.setSubject("Your new InCites\u2122 subscription", "UTF-8");
    message.setContent("hello", "text/plain");
    message.writeTo(System.out);
  }
}

输出:

Message-ID: <7888229.0.1291967222281.JavaMail.roland@bacc>
Subject: =?UTF-8?Q?Your_new_InCites=E2=84=A2_subscription?=
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

hello

您可以看到主题标题已编码，这是必要且正确的。

[更新:我修复了 Unicode 转义序列，如我的评论之一所示。]