是否可以将内联 bitmap object 添加到通过 JavaMail 发送的 email 的正文中？

Question

I'd like to add an inline bitmap (generated within the code) to an email to be sent via JavaMail in Android. Below is my code currently:

try {
            // Compose the message
            // javax.mail.internet.MimeMessage class is
            // mostly used for abstraction.
            Message message = new MimeMessage(session);

            // header field of the header.
            message.setFrom(new InternetAddress("service@someone.com"));

            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
            message.setSubject("Workside Verification Service");
            message.setText(
                    "Thank you for registering. Please click on the following link to activate your account:\n\n"
                            + urlWithToken
                            + "\n\nRegards,\nThe Workside Team");

            // Add the generated QR code bitmap here
            Multipart multipart = new MimeMultipart("related");
            MimeBodyPart imgPart = new MimeBodyPart();
            // imageFile is the file containing the image

            // TODO - pass bitmap to imageFile below
            File file = new File(null);
            OutputStream os = new BufferedOutputStream(new FileOutputStream(file));

            mBitmapQR.compress(Bitmap.CompressFormat.PNG, 90, os);


            imgPart.attachFile(imageFile);
            multipart.addBodyPart(imgPart);
            message.setContent(multipart);

            Transport.send(message); // send Message

            System.out.println("Email Sent");

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

I was thinking of converting the bitmap to a File object and then adding it to the body of the message, but I was thinking that there could be a more straightfirward and efficient way.

Answer 1

The Jakarta Mail FAQ is your best resource. See How do I send HTML mail that includes images? . That describes 3 choices:

1. Link image to web site, which I doubt works for you.
2. Inline the image <img src="data:image/jpeg;base64,base64-encoded-data-here" />
3. Construct a multipart/related message as you are doing.

Answer 2

The issue, as seen from the code, was that I was adding the text to the multipart, then the image (effectively overriding the text), and then I was assigning the multipart to the message. The solution was to add the text, using addBodyPart(text) , and then use addBodyPart(image) . After that, I could use setContent(multipart) to properly assign the text and image to the email.

    // Add the generated QR code bitmap here
    Multipart multipart = new MimeMultipart("related");
    MimeBodyPart imgPart = new MimeBodyPart();

    // Set the cache path and generate the new file image
    String mFilePath = mContext.getCacheDir().toString();
    File file = new File(mFilePath, FILE_NAME);
    OutputStream os = new BufferedOutputStream(new FileOutputStream(file));

    // TITLE
    message.setSubject("Workside Verification Service");
    // TEXT
    MimeBodyPart txtPart = new MimeBodyPart();
    txtPart.setContent("Welcome to Workside! \n\nPlease proceed by scanning the QR code provided using the Workside application available in the Google Play store.\n\n\n"
                                + "Regards,\n\nThe Workside Team", "text/plain");
    // ADD TEXT
    multipart.addBodyPart(txtPart);
    // Generate image using the QR Bitmap, and attach it
    mBitmapQR.compress(Bitmap.CompressFormat.JPEG, 90, os);
    imgPart.attachFile(mFilePath + FILE_NAME);
    // ADD IMAGE
    multipart.addBodyPart(imgPart);
    message.setContent(multipart);