Setting attachment content-type manually?

Question

Hello,
I am trying to write code that will allow a user to specify the content-type of an attachment when s/he adds it to an email. The following code, which appears to let Java figure out the content-type from the file extension, works just fine:
Multipart multipart = new MimeMultipart();
// Part one is the text
BodyPart bodyPart = new MimeBodyPart();
bodyPart.setText("Some text");
multipart.addBodyPart(bodyPart);
// Part two is the attachment
bodyPart = new MimeBodyPart();
DataSource sourceFile = new FileDataSource(FileName);
bodyPart.setDataHandler(new DataHandler(sourceFile));
multipart.addBodyPart(bodyPart);
message.setContent(multipart);
I attached a .exe file, passed the DataSource into the DataHandler constructor, and it sent the email as expected, with a Content-Type of application/octet-stream. However, if I do the following instead:
bodyPart.setContent(fileDataSource, "application/octet-stream");
-or-
bodyPart.setDataHandler(new DataHandler(fileDataSource, "application/octet-stream");
I get the dreaded javax.activation.UnsupportedDataTypeException: no object DCH for MIME type application/octet-stream. Why do I get this exception when using setContent, but not when I use the DataHandler? It seems it has the same Content-Type either way.
-Aaron

Answer 1

Well, I figured out the answer myself by digging into the source code.
When you create a DataHandler by using the (Object, String) constructor, it expects an Object that is not a DataSource, or so it would seem. So I abducted the BinaryArrayDataSource from the demo classes and instantiated one of it, specifying my desired content type and passing in the FileInputStream from the file that I was creating my FileDataSource from, and it worked like a champ.
So, the moral is, use DataSources whenever possible!
-Aaron