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:

public void addHeaderLine(String line) throws 
 MessagingException, IllegalWriteException, IllegalStateException

The getHeader( ) method returns the value of every header in the message with the given name. If there are multiple headers with this name, then the string separates the values of the different headers with the specified delimiter string:

public String getHeader(String name, String delimiter) 
 throws MessagingException

The getAllHeaderLines( ) method returns a java.util.Enumeration containing every header in the message. The Enumeration contains String objects, one per header. Each String contains the full name and value; for example, “Subject: Re: Java 2 support”. It is not divided into a separate name and value:

public Enumeration getAllHeaderLines(  ) throws MessagingException

The getMatchingHeaderLines( ) method returns all header lines whose names are given in the names argument array. The getNonMatchingHeaderLines( ) method does the same thing except that it returns all those header lines with a name not mentioned in the names argument:

public Enumeration getMatchingHeaderLines(String[] names) 
 throws MessagingException
public Enumeration getNonMatchingHeaderLines(String[] names) 
 throws MessagingException

The getEncoding( ) method returns the encoding of this MIME part as a String as given by the Content-transfer-encoding: header. The typical encoding for a plain-text email is 7-bit or perhaps 8-bit or quoted-printable. The typical encoding for a file attachment is Base64:

public String getEncoding(  ) throws MessagingException

The getContentID( ) method returns a string that uniquely identifies this part as given by the part’s Content-ID: field. A typical ID looks like <[email protected]>. It returns null if the part doesn’t have a content ID:

public String getContentID(  ) throws MessagingException
 IllegalWriteException, IllegalStateException

The getContentLanguage( ) method returns the value of the Content-language: header. This is a comma-separated list of two (or more) letter abbreviations for languages as defined by RFC 1766. For example, English is “en” and French is “fr”. It returns null if the part doesn’t have a Content-language: header.

public String[] getContentLanguage(  ) throws MessagingException

There’s also a setContentLanguage( ) method that you might use when sending a message:

public void setContentLanguage(String[] languages) throws 
 MessagingException, IllegalWriteException, IllegalStateException

Finally, the two setText( ) methods set the content of the part with the MIME type text/plain. The second setText( ) method also lets you specify the character set; for example, us-ascii or ISO 8859-1:

public void setText(String text) throws MessagingException
public void setText(String text, String charset) 
 throws MessagingException