import java.time.LocalDateTime;
import java.util.Properties;
import java.util.Random;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class OTPMail {

     static char[] OTP(int len)
        {
            System.out.println("Generating OTP using random() : ");
            // Using numeric values
            String numbers = "0123456789";
            // Using random method
            Random rndm_method = new Random();
            char[] otp = new char[len];
            for (int i = 0; i < len; i++)
            {
                // Use of charAt() method : to get character value
                // Use of nextInt() as it is scanning the value as int
                otp[i] =
                 numbers.charAt(rndm_method.nextInt(numbers.length()));
            }
            return otp;
        }
        public static void main(String[] args)
        {
            int length = 4;
            char[] OTP = OTP(length);
            System.out.print("Generated OTP is: ");
            System.out.println(OTP);
            String OTPString = String.valueOf(OTP);
            //send an email
            String messageForMail = "Your OTP for <company name>is: " + OTPString;

            //update admin mail and password here


            final String username = "shop@<ownDomain>.com";
            final String password = "<passowrd>";

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

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

            try {

                Message message = new MimeMessage(session);
                //message.setFrom(new InternetAddress("Kisna"));

                //update recipient mail id here.
                message.setRecipients(Message.RecipientType.TO,
                    InternetAddress.parse("<mailId>@gmail.com"));
                message.setSubject("OTP");
                message.setText(messageForMail);

                Transport.send(message);

                System.out.println("OTP sent to mail");
                //check the time when mail is sent

            } catch (MessagingException e) {
                throw new RuntimeException(e);
            }

        }

}