RFC822 email - Formatter - Android/iOS - create MimeMessage without session or host

Question

I have the following email:

Subject = Hello!
Body = Bla bla bla bla.
Recipients = "carlos@mail.com", "mike@mail.com"

Now I want to parse that fields following RFC822, but I can't find it.

What I need?

All fields(Subject,Body,Recipients) -> Formatter(java and/or objective-c) -> String according RC822

What I tried?

• https://code.google.com/archive/p/javamail-android/
• mime4j

The problem is they are session oriented and I don't have credentials or host.

Update

I need something like this but instead using message.writeTo(...) I want something like String dataRFC822 = message.getRFC822String();

// Recipient's email ID needs to be mentioned.
      String to = "destinationemail@gmail.com";

      // Sender's email ID needs to be mentioned
      String from = "fromemail@gmail.com";

      // Get the Session object. Which I have not and I don't want it.
      Session session = Session.getInstance(props,
         new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
               return new PasswordAuthentication(username, password);
            }
         });

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

         // Set From: header field of the header.
         message.setFrom(new InternetAddress(from));

         // Set To: header field of the header.
         message.setRecipients(Message.RecipientType.TO,
            InternetAddress.parse(to));

         // Set Subject: header field
         message.setSubject("Testing Subject");

         // Create the message part
         BodyPart messageBodyPart = new MimeBodyPart();

         // Now set the actual message
         messageBodyPart.setText("This is message body");

         // Create a multipar message
         Multipart multipart = new MimeMultipart();

         // Set text message part
         multipart.addBodyPart(messageBodyPart);

         // Part two is attachment
         messageBodyPart = new MimeBodyPart();
         String filename = "/home/manisha/file.txt";
         DataSource source = new FileDataSource(filename);
         messageBodyPart.setDataHandler(new DataHandler(source));
         messageBodyPart.setFileName(filename);
         multipart.addBodyPart(messageBodyPart);

         // Send the complete message parts
         message.setContent(multipart);

         //instead write it on a stream i I want get back the string formated according to rfc822
         message.writeTo(...);


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

Answer 1

You can manually make a RFC822 compatible string manually, if you don't attach a file or absolutely need a multipart mime message, it's way more simple:

String makeRfc822email(String from, String to, String subject, String message) {
  StringBuilder builder = new StringBuilder();
  builder.append("From: ");
  builder.append(from);
  builder.append("\n");

  builder.append("To: ");
  builder.append(to);
  builder.append("\n");

  builder.append("Subject: ");
  builder.append(subject);
  builder.append("\n\n");  // Blank line before message.

  builder.append(message);

  return builder.toString();
}

Answer 2

As @Shadowfacts pointed out, you can use a ByteArrayOutputStream.

The trick is you don't need credentials on the session object, as long as you don't really use it to connect to a server. Then I just re-used most of your code:

String to = "destinationemail@gmail.com";
String from = "fromemail@gmail.com";

// Empty properties and null credentials makes a valid session.
Properties props = new Properties();
Session session = Session.getInstance(props, null);

Message message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
message.setSubject("Testing Subject");
BodyPart messageBodyPart = new MimeBodyPart();
messageBodyPart.setText("This is message body");

Multipart multipart = new MimeMultipart();
multipart.addBodyPart(messageBodyPart);

messageBodyPart = new MimeBodyPart();
String filename = "/etc/hostname";
DataSource source = new FileDataSource(filename);
messageBodyPart.setDataHandler(new DataHandler(source));
messageBodyPart.setFileName(filename);
multipart.addBodyPart(messageBodyPart);

message.setContent(multipart);

ByteArrayOutputStream baos = new ByteArrayOutputStream();
message.writeTo(baos);
String rfc822message = baos.toString();
System.out.print(rfc822message);

The result I got:

From: fromemail@gmail.com
To: destinationemail@gmail.com
Message-ID: <392292416.1.1481815905219@nitoshpas>
Subject: Testing Subject
MIME-Version: 1.0
Content-Type: multipart/mixed; 
boundary="----=_Part_0_59559151.1481815905197"

------=_Part_0_59559151.1481815905197
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

This is message body
------=_Part_0_59559151.1481815905197
Content-Type: application/octet-stream; name="/etc/hostname"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="/etc/hostname"

nitoshpas

------=_Part_0_59559151.1481815905197--

Answer 3

You can use ByteArrayOutputStream which is an implementation of OutputStream that writes to a byte array. You can create an instance of this and pass it to writeTo(OutputStream) on your method and from there call toString on the ByteArrayOutputStream to retrieve a String representation of the message.

ByteArrayOutputStream out = new ByteArrayOutputStream();
message.writeto(out);
String s = out.toString();