import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;


public class MailDemo {
    public static void main(String[] args) {
        Properties properties=new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable","true");
        properties.put("mail.smtp.host","smtp.gmail.com");
        properties.put("mail.smtp.port", "587");
        Scanner scn=new Scanner(System.in);
        System.out.println("Username for Authentication :");
        final String username=scn.nextLine();
        System.out.println("Password for Authentication :");
        final String password=scn.nextLine();
        System.out.println("From Email..");
        String fromEmailAddrs=scn.nextLine();
        System.out.println("To Email..");
        String toEmail=scn.nextLine();
        System.out.println("Subject..");
        String subject=scn.nextLine();
        System.out.println("Message..");
        String textMessage=scn.nextLine();
        Session session=Session.getDefaultInstance(properties,new Authenticator() {
            @Override
            protected javax.mail.PasswordAuthentication getPasswordAuthentication(){
                return new javax.mail.PasswordAuthentication(username, password);
            }
        });
        try{
            Message msg=new MimeMessage(session);
            msg.setFrom(new InternetAddress(fromEmailAddrs));
            msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse(toEmail));
            msg.setSubject(subject);
            msg.setText(textMessage);
            Transport.send(msg);
            System.out.println("/n Your Message Delivered Succesfully");
        }
        catch(MessagingException m){
            throw new RuntimeException(m);
        }

    }
}

Username for Authentication :
bijaybhaskar01
Password for Authentication :
abcdef@456789
From Email..
bijaybhaskar01@gmail.com
To Email..
bbswain1001@gmail.com
Subject..
Hello
Message..
hai

Exception in thread "main" java.lang.RuntimeException: javax.mail.SendFailedException: Sending failed;
  nested exception is:
    class javax.mail.MessagingException: 530 5.7.0 Must issue a STARTTLS command first. fh14sm3131583pab.31 - gsmtp

    at com.mail.bhaskar.MailDemo.main(MailDemo.java:52)
Caused by: javax.mail.SendFailedException: Sending failed;
  nested exception is:
    class javax.mail.MessagingException: 530 5.7.0 Must issue a STARTTLS command first. fh14sm3131583pab.31 - gsmtp

    at javax.mail.Transport.send0(Transport.java:218)
    at javax.mail.Transport.send(Transport.java:80)
    at com.mail.bhaskar.MailDemo.main(MailDemo.java:48)