如何使用 java 中的 mimemessage 类获取电子邮件正文和附件

Question

在我的 SMTP 服务器代码中，我有一个 MimeMessage 实例，我想用它来提取传入的邮件正文（邮件文本）和邮件附件。为此，我在客户端和服务器端使用以下实现。但是，我只能检索邮件附件。该代码以某种方式检测到 CustomerEngineer.ahmet 两次，但它们都不包含邮件正文：“这是邮件正文”。我可以检索图像。

在我的 java 邮件客户端中，我创建了一个具有以下架构的邮件：

try {
        // Create a default MimeMessage object
        Message message = new MimeMessage(session);

        message.setFrom(new InternetAddress(from));

        message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));

        // Set Subject
        message.setSubject("Hi JAXenter");

        BodyPart messageBodyPart = new MimeBodyPart();

        messageBodyPart.setText("This is a message body");

        Multipart multipart = new MimeMultipart();

        multipart.addBodyPart(messageBodyPart);

        DataSource source = new FileDataSource(new File(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\CustomerEngineer.png")));
        messageBodyPart.setDataHandler(new DataHandler(source));
        messageBodyPart.setFileName("CustomerEngineer.ahmet");
        multipart.addBodyPart(messageBodyPart);

        message.setContent(multipart);

        // Send message
        Transport.send(message);

        System.out.println("Sent message successfully....");

    } catch (MessagingException e) {
        throw new RuntimeException(e);
    }

在我的服务器端，我使用以下逻辑：

 MimeMessage message = new MimeMessage(session, data);

public void seperateBodyAndAttachments(MimeMessage message) throws MessagingException, IOException {
    String mimeType = message.getContentType();
    Date dt = new Date();

    if (message.isMimeType("text/*")) {
        System.out.println("this containst a text file");
    }  else if (message.isMimeType("multipart/*")) {
        Multipart mp = (Multipart) message.getContent();
        int idx = 0;
        int count = mp.getCount();
        for (int i = 0; i < count; i++) {
            BodyPart part = mp.getBodyPart(i);
            String name = part.getDataHandler().getName();
            if (part.isMimeType("text/*")) {
                if (name == null) {
                    name = "text-" + (++idx) + ".txt";
                }
                System.out.println(name);
            } else {
                if (name == null) {
                    name = "attachment-" + (++idx);
                }
                FileOutputStream fos = new FileOutputStream(System.getProperty("user.dir").concat("\\src\\main\\resources\\DevEnvironmentConfigFile\\" + name));
                BufferedOutputStream bos = new BufferedOutputStream(fos);
                part.getDataHandler().writeTo(bos);
                bos.close();
            }
        }
    } else if (message.isMimeType("message/rfc822")) {
        // Not implemented
    } else {
        Object o = message.getContent();
        if (o instanceof String) {
            FileWriter fw = new FileWriter(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\downloads\\"  + "text.txt"));
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write((String)o);
            bw.close();
        } else if (o instanceof InputStream) {
            FileOutputStream fos = new FileOutputStream(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\downloads\\"  +"message.dat"));
            BufferedOutputStream bos = new BufferedOutputStream(fos);
            message.getDataHandler().writeTo(bos);
            bos.close();
        } else {
            FileWriter fw = new FileWriter(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\downloads\\"  +"unknown.txt"));
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write((String)o);
            bw.close();
        }
    }
}

Answer 1

不太确定您的电子邮件结构。但请注意，多部分可以嵌套 - 因此您必须一直向下搜索主体。而使用 mutlipart/alternative，可能会有不止一个实体。

在您的情况下，您可能正在查看

multipart/mixed
  multipart/alternative
    text/plain
    text/html
attachment

一种结构。所以第一个多部分真的不包括身体。 考虑这段代码：

public void seperateBodyAndAttachments(MimeMessage mm) throws MessagingException, IOException {
   String mimeType = message.getContentType();
   System.out.println("Message is a " + mimeType);  
   Object content = mm.getContent();
   if(content instanceof String) {
     System.out.println("Body: " + content);
   } else if(content instanceof MimeMultipart) {                
     MimeMultipart multi = (MimeMultipart)content;
     System.out.println("We have a "+ multi.getContentType());              
     for(int i = 0; i < multi.getCount(); ++i) {
        BodyPart bo = multi.getBodyPart(i);
        System.out.println("Content "+i+" is a " + bo.getContentType());
        //Now that body part could again be a MimeMultipart...
        Object bodyContent = bo.getContent();
        //possibly build a recurion here -> the logic is the same as for mm.getContent() above
      }
    } else {
        System.out.println("Some other content: " + content.getClass().getName());
    }
}

在您的情况下，混淆来自两次添加 body-part：

    // This is the object created
    BodyPart messageBodyPart = new MimeBodyPart();
    messageBodyPart.setText("This is a message body");

    Multipart multipart = new MimeMultipart();

    // you add a reference to this object into the multipart
    multipart.addBodyPart(messageBodyPart);


    DataSource source = new FileDataSource(new File(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\CustomerEngineer.png")));

    //you CHANGE THE CONTENTS of the object to now contain your attachment
    messageBodyPart.setDataHandler(new DataHandler(source));
    messageBodyPart.setFileName("CustomerEngineer.ahmet");

    //and add it a second time.
    multipart.addBodyPart(messageBodyPart);

也许试试这个发送：

        // Set Subject
        message.setSubject("Hi JAXenter");


        Multipart multipart = new MimeMultipart("mixed");
        //Add Text Part         
        BodyPart textBodyPart = new MimeBodyPart();
        textBodyPart.setContent("This is a message body", "text/plain");
        multipart.addBodyPart(textBodyPart);

        //Add attachment
        DataSource source = new FileDataSource(new File(System.getProperty("user.dir").concat("\\src\\main\\java\\emailrelayserver\\CustomerEngineer.png")));
        BodyPart messageBodyPart = new MimeBodyPart();
        messageBodyPart.setDataHandler(new DataHandler(source));
        messageBodyPart.setFileName("CustomerEngineer.ahmet");
        multipart.addBodyPart(messageBodyPart);

        //Set this as message content
        message.setContent(multipart);



        //This will show you internal structure of your message! D
        message.saveChanges();
        message.writeTo(System.out);

        Transport.send(message);            

Answer 2

就我而言，我需要从MimeMessage 中提取MimeBodyPart。这比我想象的要棘手，但我最终从BouncyCastle 抢走了这两种方法

 /**
 * extract an appropriate body part from the passed in MimeMessage
 */
protected MimeBodyPart makeContentBodyPart(
    MimeMessage message)
    throws SMIMEException
{
    MimeBodyPart content = new MimeBodyPart();
    //
    // add the headers to the body part.
    //
    try
    {
        message.removeHeader("Message-Id");
        message.removeHeader("Mime-Version");

        // JavaMail has a habit of reparsing some content types, if the bodypart is
        // a multipart it might be signed, we rebuild the body part using the raw input stream for the message.
        try
        {
            if (message.getContent() instanceof Multipart)
            {
                content.setContent(message.getRawInputStream(), message.getContentType());
                extractHeaders(content, message);
                return content;
            }
        }
        catch (MessagingException e)
        {
            // fall back to usual method below
        }
        content.setContent(message.getContent(), message.getContentType());
        content.setDataHandler(message.getDataHandler());
        extractHeaders(content, message);
    }
    catch (MessagingException e)
    {
        throw new SMIMEException("exception saving message state.", e);
    }
    catch (IOException e)
    {
        throw new SMIMEException("exception getting message content.", e);
    }

    return content;
}

private void extractHeaders(MimeBodyPart content, MimeMessage message)
    throws MessagingException
{
    Enumeration e = message.getAllHeaders();

    while (e.hasMoreElements())
    {
        Header hdr = (Header)e.nextElement();
        content.addHeader(hdr.getName(), hdr.getValue());
    }
}