The following code is supposed to send email via gmail but it gives the following error:

![enter image description here](https://i.stack.imgur.com/DnGoq.jpg)

On my gmail account I get a message that a sign in was prevented and I should use a secure app like gmail to access my account. The source code is as shown below:

```
public void doSendMail(){
    username = txtFrom.getText();
    password= new String(txtPassword.getPassword());
    to = txtTo.getText();
    subject = txtSubject.getText();
    email_body = jTextArea1.getText();

    Properties props = new Properties();
    props.put("mail.smtp.host", "smtp.gmail.com");
    props.put("mail.smtp.socketFactory.port", "587");
    props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.smtp.port", "587");

    Session session = Session.getDefaultInstance(props,
            new javax.mail.Authenticator(){
                @Override
                protected PasswordAuthentication getPasswordAuthentication(){
                    return new PasswordAuthentication(username, password);
                }
    }
    );
    try {
        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress(username));
        message.setRecipients(Message.RecipientType.TO,InternetAddress.parse(to));
        message.setSubject(subject);
        message.setText(email_body);
        Transport.send(message);

        JOptionPane.showMessageDialog(this, "Message Sent!","Sent",JOptionPane.INFORMATION_MESSAGE);

    } catch (Exception e) {
        JOptionPane.showMessageDialog(this, e.toString());
    }
}

```

What can I do to the code to make it send mail via gmail?