Transport.send()在邮件地址无效时的行为

当使用JavaMail API中的Transport类的send()方法发送邮件时，如果邮件地址无效，则会抛出AddressException异常。因此，可以使用try-catch块来捕获该异常并进行处理，如下所示：

import javax.mail.*;
import javax.mail.internet.*;

public class MailSender {
    public static void sendEmail(String toAddress) {
        String fromAddress = "example@gmail.com";
        String mailBody = "This is a test email";
        String mailSubject = "Test Email";
        String smtpHost = "smtp.gmail.com";
        String smtpUsername = "example@gmail.com";
        String smtpPassword = "password";

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

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

        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(fromAddress));
            message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse(toAddress));
            message.setSubject(mailSubject);
            message.setText(mailBody);

            Transport.send(message);

            System.out.println("Email sent successfully.");
        } catch (AddressException e) {
            System.out.println("Invalid email address.");
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

在sendEmail()方法中使用try-catch块来捕获AddressException异常，并在控制台上输出“无效的电子邮件地址”。通过这种方法，您可以更准确地了解邮件发送中出现的问题并进行相应的处理。