Multi-byte characters in attachment filename

I am retrieving attachments in emails using JavaMail APIs. However, if the attachment filename has multi-byte characters in it, i get ? or something like "=?utf-8?B?5byM5L6I5YaJLmRvYw==?=". I tried-

1. String filename = part.getFileName()

2. String filename = MimeUtility.decodeText(part.getFileName());

3. Setting the system property: System.setProperty("mail.mime.decodefilename", "true");

But none of the methods return correct attachmnet name with japanese characters. Please help.

[520 byte] By [neha_83a] at [2007-11-26 19:34:49]