Java通过gmail发送电子邮件，有时工作有时挂起

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;

public class SendEmail {
    public static void main(String[] args) {
        // 配置SMTP服务器
        String host = "smtp.gmail.com";
        int port = 465;
        String username = "your-email@gmail.com";
        String password = "your-password";

        // 创建Properties对象
        Properties props = new Properties();
        props.put("mail.smtp.host", host);
        props.put("mail.smtp.port", port);
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.ssl.enable", "true");

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

        try {
            // 创建Message对象
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(username));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("recipient-email@example.com"));
            message.setSubject("Hello from JavaMail");
            message.setText("This is a test email.");

            // 发送邮件
            Transport.send(message);

            System.out.println("Email sent successfully.");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}