如@ scary-wombat所述，您没有添加第一个参数.我想你打算这样做:

As @scary-wombat mentioned, you didn't add the first par. I suppose you meant to do:

        ...
        // add it
        multipart.addBodyPart(messageBodyPart);
        // second part (the image)
        ...

您还可以将Content-Disposition标头添加到图像部分:

You can also add a Content-Disposition header to the image part:

messageBodyPart.setDisposition(MimeBodyPart.INLINE);

更新:

对不起，您还必须向上移动多部分的创建:

Sorry, you must also move up the creation of multipart:

        ...
        // add it
        MimeMultipart multipart = new MimeMultipart("related");
        multipart.addBodyPart(messageBodyPart);
        // second part (the image)
        ...

更新2:

尝试一下:

          BodyPart messageBodyPart = new MimeBodyPart();
          String htmlText = "<H1>Hello</H1><img src=\"cid:image\">";
          messageBodyPart.setContent(htmlText, "text/html");
          // add it
         MimeMultipart multipart = new MimeMultipart("related");

         multipart.addBodyPart(messageBodyPart);

        // second part (the image)
          messageBodyPart = new MimeBodyPart();

          java.io.InputStream inputStream = this.getClass().getResourceAsStream("/HappyBirthday.JPG");
         ByteArrayDataSource ds = new ByteArrayDataSource(inputStream, "image/jpg");
         System.out.println(inputStream);

          messageBodyPart.setDataHandler(new DataHandler(ds));
          messageBodyPart.setHeader("Content-ID", "<image>");

          messageBodyPart.setDisposition(MimeBodyPart.INLINE);

         multipart.addBodyPart(messageBodyPart);
         message.setContent(multipart);  
         // Send message
         Transport.send(message);