public class MailSender {

    private final static  String USERNAME = "mail-box adres";
    private final static String PASSWORD = "mail-box password";

    Connection connection;

    public MailSender(Connection connect) {
        connection=connect;
    }

    public  void send(List<Message> messageList) throws MessagingException {
        if (messageList==null) throw new NullPointerException("Message error");

        MailRepository dataModificator=new MailRepository(connection);

        Properties props = new Properties();
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.host", "smtp.gmail.com");
        props.put("mail.smtp.port", "587");
        props.put("mail.smtp.ssl.trust", "smtp.gmail.com");

        Session session = Session.getInstance(props,
                new javax.mail.Authenticator() {
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(USERNAME, PASSWORD);
                    }
                });

public class MyClass {

    private static final Properties props = new Properties(){{
        put("mail.smtp.starttls.enable", "true");
        put("mail.smtp.auth", "true");
        put("mail.smtp.host", "smtp.gmail.com");
        put("mail.smtp.port", "587");
        put("mail.smtp.ssl.trust", "smtp.gmail.com");
    }};

}