java如何实现发送带存储在服务器的附件的邮件

要在Java中发送带附件的邮件，可以使用JavaMail API。以下是一个示例代码，可以实现将附件添加到邮件中并发送邮件：

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

public class SendEmailWithAttachment {
    public static void main(String[] args) {
        // 邮件信息
        String host = "smtp.example.com";
        String from = "your-email@example.com";
        String password = "your-email-password";
        String to = "recipient@example.com";
        String subject = "Email with Attachment";
        String body = "Please see the attached file.";

        // 附件信息
        String filename = "file.txt";
        String filepath = "/path/to/file.txt";

        // 设置邮件属性
        Properties props = new Properties();
        props.put("mail.smtp.host", host);
        props.put("mail.smtp.auth", "true");

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

        try {
            // 创建邮件对象
            MimeMessage message = new MimeMessage(session);
            message.setFrom(new InternetAddress(from));
            message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse(to));
            message.setSubject(subject);

            // 创建邮件内容
            Multipart multipart = new MimeMultipart();
            BodyPart messageBodyPart = new MimeBodyPart();
            messageBodyPart.setText(body);
            multipart.addBodyPart(messageBodyPart);

            // 创建附件
            messageBodyPart = new MimeBodyPart();
            DataSource source = new FileDataSource(filepath);
            messageBodyPart.setDataHandler(new DataHandler(source));
            messageBodyPart.setFileName(filename);
            multipart.addBodyPart(messageBodyPart);

            // 设置邮件内容
            message.setContent(multipart);

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

            System.out.println("Email with Attachment sent successfully!");
        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

需要注意的是，这个示例代码中的邮件服务器地址、发件人邮箱、发件人邮箱密码、收件人邮箱、附件文件名和附件文件路径需要根据实际情况进行修改。