title: Send calendar invite per email with java
body: <p>I'm trying to send calendar invites per email with java. The recipient gets the email but instead of being shown an invitation to accept or decline, the event is automatically added to his calendar.</p>
  
  <p>I'm building the event/invite with ical4j.jar</p>
  
  <pre><code>private Calendar getInvite(Session session) {
      Calendar calendar = new Calendar();
      calendar.getProperties().add(Version.VERSION_2_0);
      calendar.getProperties().add(Method.REQUEST);
  
      VEvent event = new VEvent(
          new DateTime(sesion.getStartDate()), 
          new DateTime(sesion.getEndDate()), 
          session.getName());
  
      event.getProperties().add(Priority.MEDIUM);
      event.getProperties().add(Clazz.PUBLIC);
  
      try {
          UidGenerator ug = new UidGenerator("uidGen");
          Uid uid = ug.generateUid();
          event.getProperties().add(uid);
      } catch (SocketException e) {
          // Log things
      }
  
      for (Participant participant : session.getParticipants()) {
          Attendee attendee = new Attendee(URI.create("mailto:" + participant.getEmail()));
          attendee.getParameters().add(Role.OPT_PARTICIPANT);
          attendee.getParameters().add(new Cn(participant.getName()));
          attendee.getParameters().add(PartStat.NEEDS_ACTION);
          event.getProperties().add(attendee);
      }
  
      calendar.getComponents().add(event);
  
      return calendar;
  
  }
  </code></pre>
  
  <p>And this is how I send the email:</p>
  
  <pre><code>public void sendEmail(String fromMail, String toMail, String subject, String text, net.fortuna.ical4j.model.Calendar calendar) {
      try {
          Session session = Session.getInstance(getMailProperties(), new javax.mail.Authenticator() {
              protected PasswordAuthentication getPasswordAuthentication() {
                  return new PasswordAuthentication(getUser(), getPassword());
              }
          });
  
          MimeMessage mimeMessage = new MimeMessage(session);
          mimeMessage.setHeader("Content-Transfer-Encoding:", "7bit");
  
          Address address = new InternetAddress(fromMail);
          mimeMessage.setFrom(address);
  
          mimeMessage.setSentDate(Calendar.getInstance().getTime());
          mimeMessage.setRecipients(Message.RecipientType.TO, toMail);
  
          mimeMessage.setSubject(subject);
          Calendar cal = Calendar.getInstance();
          mimeMessage.setSentDate(cal.getTime());
  
          Multipart multipart = new MimeMultipart("alternative");
  
          // First part - HTML readable text  
          MimeBodyPart msgHtml = new MimeBodyPart();
          msgHtml.setContent(text, "text/html; charset=UTF-8");
  
          multipart.addBodyPart(msgHtml);
  
          if (calendar != null) {
              // Another part for the calendar invite
              MimeBodyPart invite = new MimeBodyPart();
              invite.setHeader("Content-Class", "urn:content-  classes:calendarmessage");
              invite.setHeader("Content-ID", "calendar_message");
              invite.setHeader("Content-Disposition", "inline");
              invite.setContent(calendar.toString(), "text/calendar");
              multipart.addBodyPart(invite);
          }
  
          mimeMessage.setContent(multipart);
  
          Transport.send(mimeMessage);
  
      } catch (Exception e) {
          // Log things
      }
  
  }
  </code></pre>
  
  <p>But when I get the email (in gmail), I see no invitation, the event is automatically added to my calendar. I can only accept or decline by clicking on the event in the calendar.</p>
  
  <p>I have tried to just send the invite, then what happens is that I get an email with an ics attachment.</p>
  
  <p>What am I missing?</p>