使用javamail将字符串作为附件发送会得到重复的内容

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

public class EmailSender {
    public static void main(String[] args) {
        // 邮件服务器配置
        String host = "smtp.example.com";
        String username = "your_username";
        String password = "your_password";

        // 发件人和收件人信息
        String from = "sender@example.com";
        String to = "recipient@example.com";

        // 创建邮件会话
        Properties props = new Properties();
        props.put("mail.smtp.host", host);
        props.put("mail.smtp.auth", "true");
        Session session = Session.getInstance(props, new Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        try {
            // 创建邮件消息
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
            message.setSubject("附件邮件");

            // 创建附件
            MimeBodyPart attachment = new MimeBodyPart();
            attachment.setText("这是附件内容");

            // 将附件添加到邮件中
            Multipart multipart = new MimeMultipart();
            multipart.addBodyPart(attachment);
            message.setContent(multipart);

            // 发送邮件
            Transport.send(message);
            System.out.println("邮件发送成功");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}