how to send HTML email

I have to send HTML file via email but not as attachment.

Message simpleMessage = new MimeMessage(mailSession);
try {
   fromAddress = new InternetAddress(from);
   toAddress = new InternetAddress(to);

} catch (AddressException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
}

try {
    simpleMessage.setFrom(fromAddress);
    simpleMessage.setRecipient(RecipientType.TO, toAddress);

    simpleMessage.setSubject(subject);
    simpleMessage.setText(text);

    Transport.send(simpleMessage);
} catch (MessagingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

It is sending email simply with text message. I want to send HTML content which is stored in another file but not as attachment

Don't upcast your MimeMessage to Message:

MimeMessage simpleMessage = new MimeMessage(mailSession);

Then, when you want to set the message body, either call

simpleMessage.setText(text, "utf-8", "html");

or call

simpleMessage.setContent(text, "text/html; charset=utf-8");

If you'd rather use a charset other than utf-8, substitute it in the appropriate place.

JavaMail has an extra, useless layer of abstraction that often leaves you holding classes like Multipart, Message, and Address, which all have much less functionality than the real subclasses (MimeMultipart, MimeMessage, and InternetAddress) that are actually getting constructed...