Mailer application was created to have a library to send mail.

The application has default servlet MailServlet and library part, that contains files 'Constants', 'MailAuthentificator', 'MailMessage'

The example of usage is in the MailerServlet, this is simple to use library:

MailMessage mailMessage = new MailMessage(
  getContextParam(PROP_MAIL_FROM),
  recipients,
  subject,
  message
);
mailMessage.setFilesToSend(getParts(request));
String user = getContextParam(PROP_MAIL_USER);

Session session;
if (user == null || user.isEmpty()) {
  session = Session.getInstance(properties);
} else {
  session = Session.getInstance(
    properties,
    new MailAuthenticator(user, getContextParam(PROP_MAIL_PASSWORD))
  );
}
mailMessage.send(mailMessage.buildMessage(session));

1. Step one is to create MailMessage object with all parameters. It has variability to construct object and methods to set files and add recipients.

MailMessage mailMessage = new MailMessage(
  getContextParam(PROP_MAIL_FROM),
  recipients,
  subject,
  message
);
 mailMessage.setFilesToSend(getParts(request));

2. Second part is - create Session from javax.mail package. In servlet, used this construction to create session if there is user parameter in web.xml, or not

String user = getContextParam(PROP_MAIL_USER);
Session session;

if (user == null || user.isEmpty()) {
  session = Session.getInstance(properties);
} else {
  session = Session.getInstance(
    properties,
    new MailAuthenticator(user, getContextParam(PROP_MAIL_PASSWORD))
  );
}

3. Last part is building and sending mail

MimeMessage mail = mailMessage.buildMessage(session);
mailMessage.send(mail);