If this is a client application you can take a look at the java.awt.Desktop
class.
From the javadoc...
Launches the mail composing window of the user default mail client, filling the message fields specified by a mailto: URI.
A mailto: URI can specify message fields including "to", "cc", "subject", "body", etc. See The mailto URL scheme (RFC 2368) for the mailto: URI specification details.
This doesn't allow you to attach a file, but it will open up the user's mail client.
This link may be helpful... Using the Desktop API in Java SE 6