通过apache common java api转发带有附件的电子邮件（使用JavaMailApi阅读）

Question

我正在从Outlook网络邮件中读取邮件，并获取邮件列表（'javax.mail.Message'）。现在，我想使用Java程序将这些消息转发到另一个电子邮件地址。

    private void sendTestMail(String from, String subject, String sentDate, Object object, Message message)
            throws EmailException, Exception {

        MultiPartEmail email = new MultiPartEmail();
        email.setHostName(forwardHost);

        email.addTo(mailRecipients(to));
        email.setFrom(emailFrom);
        email.setSubject(subject);
        email.setMsg("Testing email by sahil.");

        EmailAttachment attachment = new EmailAttachment();
        attachment.setPath("c:\\sahil\\test.jpg");
        attachment.setDisposition(EmailAttachment.ATTACHMENT);
        attachment.setDescription("Picture_of_John");
        attachment.setName("John.jpg");
        email.attach(attachment);  


        MimeMultipart multiPart = getMimeMultipart(message);
        email.addPart(multiPart);

        email.send();
    }   

如果我在上面的代码的两行下面注释，则可以正常工作。

MimeMultipart multiPart = getMimeMultipart(message);
email.addPart(multiPart);

但是有了这两行，我就异常了。

2020-04-20 15:41:44,271 ERROR com.st.ict.ols.service.impl.ReplyToMessageServiceImpl [main]  Inner Exception occurred while processing individual message. Error stacktrace is[org.apache.commons.mail.EmailException: Sending the email to the following server failed : smtpapp1.sgp.st.com:25
    at org.apache.commons.mail.Email.sendMimeMessage(Email.java:1421)
    at org.apache.commons.mail.Email.send(Email.java:1448)
    at com.st.ict.ols.service.impl.ReplyToMessageServiceImpl.sendTestMail(ReplyToMessageServiceImpl.java:342)
    at com.st.ict.ols.service.impl.ReplyToMessageServiceImpl.processMessage(ReplyToMessageServiceImpl.java:167)
    at com.st.ict.ols.service.impl.MessageServiceImpl.processMessage(MessageServiceImpl.java:22)
    at com.st.ict.ols.OlsMailSenderApplication.run(OlsMailSenderApplication.java:36)
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:732)
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:716)
    at org.springframework.boot.SpringApplication.afterRefresh(SpringApplication.java:703)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:304)
    at com.st.ict.ols.OlsMailSenderApplication.main(OlsMailSenderApplication.java:27)
Caused by: javax.mail.MessagingException: IOException while sending message;
  nested exception is:
    java.io.IOException: Exception writing Multipart
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1308)
    at javax.mail.Transport.send0(Transport.java:255)
    at javax.mail.Transport.send(Transport.java:124)
    at org.apache.commons.mail.Email.sendMimeMessage(Email.java:1411)
    ... 10 more
Caused by: java.io.IOException: Exception writing Multipart
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:83)
    at javax.activation.ObjectDataContentHandler.writeTo(DataHandler.java:884)
    at javax.activation.DataHandler.writeTo(DataHandler.java:317)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1652)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:961)
    at javax.mail.internet.MimeMultipart.writeTo(MimeMultipart.java:553)
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:81)
    at javax.activation.ObjectDataContentHandler.writeTo(DataHandler.java:884)
    at javax.activation.DataHandler.writeTo(DataHandler.java:317)
    at javax.mail.internet.MimeBodyPart.writeTo(MimeBodyPart.java:1652)
    at javax.mail.internet.MimeMessage.writeTo(MimeMessage.java:1850)
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1259)
    ... 13 more
Caused by: javax.mail.MessagingException: Empty multipart: multipart/mixed; 
    boundary="----=_Part_1_1176580790.1587377502798"
    at javax.mail.internet.MimeMultipart.writeTo(MimeMultipart.java:548)
    at com.sun.mail.handlers.multipart_mixed.writeTo(multipart_mixed.java:81)
    ... 24 more

我编写的用于从JavaMailApi的Message对象中检索MimeMultipart的代码，使用附加功能在apache common的org.apache.commons.mail.MultiPartEmail对象中进行设置。

    public MimeMultipart getMimeMultipart(Message message) throws Exception {
        Object content = message.getContent();
        if (content instanceof String)
            return null;        

        if (content instanceof MimeMultipart) {
            MimeMultipart multiPartResult = new MimeMultipart();
            MimeMultipart multiPart = (MimeMultipart) content;

            List<BodyPart> result = new ArrayList<>();
            for (int i = 0; i < multiPart.getCount(); i++) {
                BodyPart bodyPart = (BodyPart) multiPart.getBodyPart(i);
                result.addAll(getMimeMultipart(bodyPart));
            }
            for(BodyPart part:result) {
                multiPart.addBodyPart(part);
            }
            return multiPartResult;

        }
        return null;
    }

    private List<BodyPart> getMimeMultipart(BodyPart part) throws Exception{
        List<BodyPart> result = new ArrayList<>();
        Object content = part.getContent();

        if (content instanceof InputStream || content instanceof String) {
            if (Part.ATTACHMENT.equalsIgnoreCase(part.getDisposition()) || StringUtils.isNotBlank(part.getFileName())) {
                result.add(part);
            }
            return result;
        }

        if (content instanceof MimeMultipart) {
                MimeMultipart multipart = (MimeMultipart) content;
                for (int i = 0; i < multipart.getCount(); i++) {
                    BodyPart bodyPart =  (BodyPart) multipart.getBodyPart(i);
                    result.addAll(getMimeMultipart(bodyPart));
                }
        }
        return result;
    }

我能够转发不包括附件的电子邮件，但在转发附件/内嵌图像时遇到问题。请帮助我解决这个问题。

我能够将完整的邮件作为附件转发，如何按原样转发消息。

MultiPartEmail email = new MultiPartEmail();
MimeMultipart mp = new MimeMultipart();
MimeBodyPart fmbp = new MimeBodyPart();
fmbp.setContent(message, "message/rfc822");
fmbp.setDisposition(Part.INLINE);
mp.addBodyPart(fmbp);
email.setContent(mp);

或者如果我使用代码

MimeMultipart mp = (MimeMultipart) message.getContent();
email.setContent(mp, message.getContentType());

我正在转发这样的电子邮件screenshot of forwarded encoded mail

Answer 1

在这种情况下，是在同一应用程序中从一个邮件服务器读取邮件并将同一邮件发送到另一电子邮件ID。

为了实现这一点，我使用Java Mail API进行读取和发送。如果两个步骤都使用不同的主机，请确保更新属性。

    private void sendMailJavax(Message oldMessage) {
        try { 
            // creating a new message using the older message
            MimeMessage message = new MimeMessage((MimeMessage)oldMessage);
            // updating properties as per sender Mailing API
            message.getSession().getProperties().clear();
            message.getSession().getProperties().setProperty("mail.smtp.host", forwardHost);

            // setting appropriate headers. // make sure you don't append using .add methods.
            message.setFrom(new InternetAddress(emailFrom));
            message.setRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setReplyTo(new Address[] { new InternetAddress(replyToEmail)});

            Transport.send(message); 
            System.out.println("Email Sent  successfully...."); 
            } catch (MessagingException mex) { 
                mex.printStackTrace(); 
            } 
    }