Processing Javamail emails for specific mime types

I recently had to write some software that received an email and processed it for iCal events. I wanted my program to be tolerant of receiving the iCal events within the body or as a attachment. Furthermore if the attachment was a mail message then I wanted to look inside that email for the event and so on...

When I thought about the problem initially I thought that processing just the attachments of an email would be sufficient. That's not the case given Microsoft Outlook though. I quickly learnt that Outlook sends its iCal events within the body of an email and not as an attachment.

I ended up with the following bit of Javamail/iCal4j/Java code that should generally be useful for processing mail messages. In my case I'm looking for a text/calendar object but it could be anything of course. The addCalendarDataToCalendars function can be called recursively and adds any calendar objects it finds to the collection passed in. Enjoy.

  /**
   * Process a data handler's content looking for a 
   * calendar object.
   * 
   * @param calendars
   *            the collection of calendars that we 
   *            must add any found calendar to.
   * @param dataHandler
   *            the data handler to use.
   */
  private void addCalendarDataToCalendars(
      Collection calendars,
      DataHandler dataHandler) {
    MimeType mimeType;
    try {
      mimeType = 
        new MimeType(dataHandler.getContentType());

      if (mimeType.getBaseType()
            .equals("text/calendar")) {
        // Calendar data is what we're ultimately 
        // searching for.
        CalendarBuilder builder = 
          new CalendarBuilder();
        Calendar calendar = builder.build(
          dataHandler.getInputStream());
        calendars.add(calendar);

      } else if (mimeType.getBaseType()
                   .equals("message/rfc822")) {
        // Found an object representing an email 
        // address in its entirety.
        Message mailMessage = (Message) dataHandler
            .getContent();
        addCalendarDataToCalendars(calendars, 
          mailMessage.getDataHandler());

      } else if (mimeType.getBaseType()
                   .startsWith("multipart/")) {
        // Found a bunch of attachments so 
        // process them each.
        Multipart multipart = 
          (Multipart) dataHandler.getContent();
        for (int i = 0, n = multipart.getCount(); 
             i < n; ++i) {
          Part part = multipart.getBodyPart(i);

          String disposition = 
            part.getDisposition();

          if ((disposition != null)
             && ((disposition.equals(Part.ATTACHMENT) 
             || (disposition.equals(Part.INLINE))))) {
            addCalendarDataToCalendars(calendars, 
              part.getDataHandler());

          } else if (disposition == null) {
            MimeBodyPart mimeBodyPart = 
              (MimeBodyPart) part;
            addCalendarDataToCalendars(calendars, 
              mimeBodyPart.getDataHandler());

          }
        }
      }

    } catch (MimeTypeParseException e) {
      logger
          .warn("Ignoring attachment - could not " +
                "parse the mime type of: "
              + dataHandler.getContentType()
              + " - " + e);
    } catch (IOException e) {
      logger.error(e);
    } catch (ParserException e) {
      logger
          .warn("Ignoring attachment - could not " +
                "interpret the calendar object: "
              + dataHandler.getName() + " - " + e);
    } catch (MessagingException e) {
      logger
          .warn("Ignoring attachment - could not " +
              "decode the calendar object: "
              + MimeUtility.getEncoding(dataHandler) 
              + " - " + e);
    }
  }