Java Network Programming, Second Edition

MIME Messages

MIME was designed mainly for Internet email, and it was specifically organized so that it would 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 seventy public and protected methods. However, with the natural exception of the constructors, almost all of these either override methods from the Message superclass or implement methods declared by the Part interface. The only new methods are a baker’s dozen declared in the MimePart interface, a subinterface of Part:

public interface MimePart extends Part

Most of these methods are very similar to either methods in Part or methods in Message. However, they have features that are unlikely to be found in non-MIME messages. For instance, a MIME part may have an MD5 digest, which would be encoded as an extra header inside the part. Thus, the MimePart interface declares and the MimeMessage class implements two methods to set and get this digest:

public String getContentMD5(  ) throws MessagingException
public void   setContentMD5(String md5) throws MessagingException, 
 IllegalWriteException, IllegalStateException

The addHeaderLine( ) method adds a string of text to the header of the message. It’s up to you to make sure that this string will actually make sense in the header: ...