Call MimeMessage.saveChanges()
on the enclosing message, which will update the headers by cascading down the MIME structure into a call to MimeBodyPart.updateHeaders()
on your body part. It's this updateHeaders
call that transfers the content type from the DataHandler
to the part's MIME Content-Type
header.
When you set the content of a MimeBodyPart
, JavaMail internally (and not obviously) creates a DataHandler
object wrapping the object you passed in. The part's Content-Type
header is not updated immediately.
There's no straightforward way to do it in your test program, since you don't have a containing MimeMessage
and MimeBodyPart.updateHeaders()
isn't public
.
Here's a working example that illuminates expected and unexpected outputs:
public class MailTest {
public static void main( String[] args ) throws Exception {
Session mailSession = Session.getInstance( new Properties() );
Transport transport = mailSession.getTransport();
String text = "Hello, World";
String html = "<h1>" + text + "</h1>";
MimeMessage message = new MimeMessage( mailSession );
Multipart multipart = new MimeMultipart( "alternative" );
MimeBodyPart textPart = new MimeBodyPart();
textPart.setText( text, "utf-8" );
MimeBodyPart htmlPart = new MimeBodyPart();
htmlPart.setContent( html, "text/html; charset=utf-8" );
multipart.addBodyPart( textPart );
multipart.addBodyPart( htmlPart );
message.setContent( multipart );
// Unexpected output.
System.out.println( "HTML = text/html : " + htmlPart.isMimeType( "text/html" ) );
System.out.println( "HTML Content Type: " + htmlPart.getContentType() );
// Required magic (violates principle of least astonishment).
message.saveChanges();
// Output now correct.
System.out.println( "TEXT = text/plain: " + textPart.isMimeType( "text/plain" ) );
System.out.println( "HTML = text/html : " + htmlPart.isMimeType( "text/html" ) );
System.out.println( "HTML Content Type: " + htmlPart.getContentType() );
System.out.println( "HTML Data Handler: " + htmlPart.getDataHandler().getContentType() );
}
}
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