Messages and Parts - JavaMail API - page 61

Attaching files (or other documents) to messages you send is more complicated. To
attach a file to a message, you first have to wrap the data in a BodyPart object and add
it to the Multipart using one of the two addBodyPart() methods:
public void addBodyPart ( BodyPart part )
throws IllegalWriteException , MessagingException
public void addBodyPart ( BodyPart part , int index )
throws IllegalWriteException , MessagingException
The first variant simply appends the part to the end of the message. The second variant
adds the given part at the specified position. If the position is greater than the number
of parts in the message, the part is simply added to the end. If it's added somewhere in
the middle, this may cause the positions of other parts to change. If the message can't
be changed, an IllegalWriteException is thrown.
The tricky part is creating the BodyPart object. You first need to guess a reasonable
MIME content type for the file ( text/plain and application/octet-stream are the
most common types). Next, read the file and convert it into some class of Java object.
Then install a javax.activation.DataHandler class that knows how to convert your
data class according to your chosen MIME type. Once you've done all this, you can
create a new MimeBodyPart object and use the various methods of the Part interface to
set attributes such as the filename and the content disposition.
There are also two removeBodyPart() methods that delete a specified part from the
message, although these aren't as commonly used:
public boolean removeBodyPart ( BodyPart part )
throws IllegalWriteException , MessagingException
public void removeBodyPart ( int index )
throws IndexOutOfBoundsException , MessagingException
If the message can't be changed, an IllegalWriteException is thrown. If the specified
index doesn't identify a part, an IndexOutOfBoundsException is thrown. If the specified
part isn't present in the message, a MessagingException is thrown.
MIME Messages
MIME was designed mainly for Internet email and specifically organized to be
backward-compatible with existing protocols and software. Therefore, a typical Internet
email message is in fact a MIME message. The only concrete subclass of Message in the
JavaMail API is javax.mail.internet.MimeMessage :
public class MimeMessage extends Message implements MimePart
This class declares almost 70 public and protected methods. However, almost all of these
either override methods from the Message superclass or implement methods declared