Java可以通過使用JavaMail API實現定期發送郵件的功能。下面是一個簡單的示例代碼：

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

public class EmailScheduler {
    private Timer timer;

    public EmailScheduler() {
        timer = new Timer();
    }

    public void scheduleEmail(String recipient, String subject, String message, Date date) {
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                // 發送郵件
                sendEmail(recipient, subject, message);
            }
        }, date);
    }

    private void sendEmail(String recipient, String subject, String message) {
        String sender = "your-email@example.com"; // 發送者郵箱
        String password = "your-password"; // 發送者郵箱密碼

        Properties props = new Properties();
        props.setProperty("mail.smtp.host", "smtp.example.com"); // SMTP服務器地址
        props.setProperty("mail.smtp.auth", "true");

        Session session = Session.getInstance(props, new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(sender, password);
            }
        });

        try {
            // 創建郵件消息
            MimeMessage mimeMessage = new MimeMessage(session);
            mimeMessage.setFrom(new InternetAddress(sender));
            mimeMessage.addRecipient(Message.RecipientType.TO, new InternetAddress(recipient));
            mimeMessage.setSubject(subject);
            mimeMessage.setText(message);

            // 發送郵件
            Transport.send(mimeMessage);
            System.out.println("郵件已發送");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        EmailScheduler scheduler = new EmailScheduler();

        // 在指定日期時間發送郵件
        Calendar calendar = Calendar.getInstance();
        calendar.set(2022, Calendar.JANUARY, 1, 10, 0, 0);
        Date date = calendar.getTime();
        scheduler.scheduleEmail("recipient@example.com", "定期郵件", "這是一封定期發送的郵件", date);
    }
}

上述示例代碼使用了java.util.Timer類來定時發送郵件。scheduleEmail方法可以指定要發送郵件的收件人、主題、內容以及發送的日期時間。通過sendEmail方法使用JavaMail API發送郵件。

請注意替換代碼中的sender、password和smtp.example.com等信息為你自己的實際郵箱信息和SMTP服務器地址。