How to attach multiple files to an email using JavaMail?

在 java 的世界裡要寄Email＋附件還滿簡單的，sample code 如下：

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

public class MailProjectClass {

public static void main(String[] args) {

    final String username = "[email protected]";
    final String password = "your.password";

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

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

    try {

        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress("[email protected]"));
        message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("[email protected]"));
        message.setSubject("Testing Subject");
        message.setText("PFA");

        MimeBodyPart messageBodyPart = new MimeBodyPart();

        Multipart multipart = new MimeMultipart();

        messageBodyPart = new MimeBodyPart();
        String file = "path of file to be attached";
        String fileName = "attachmentName";
        DataSource source = new FileDataSource(file);
        messageBodyPart.setDataHandler(new DataHandler(source));
        messageBodyPart.setFileName(fileName);
        multipart.addBodyPart(messageBodyPart);

        message.setContent(multipart);

        System.out.println("Sending");

        Transport.send(message);

        System.out.println("Done");

    } catch (MessagingException e) {
        e.printStackTrace();
    }
  }
}

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需要增加多個附件的 sample code:

private static void addAttachment(Multipart multipart, String filename)
{
    DataSource source = new FileDataSource(filename);
    BodyPart messageBodyPart = new MimeBodyPart();        
    messageBodyPart.setDataHandler(new DataHandler(source));
    messageBodyPart.setFileName(filename);
    multipart.addBodyPart(messageBodyPart);
}

Then from your main code, just call:

addAttachment(multipart, "file1.txt");
addAttachment(multipart, "file2.txt");

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如果不想 create file 再用 DataSource 去選 file，可以用這一個 sample:

how to attach file without creating file
https://stackoverflow.com/questions/3556091/javamail-problem-how-to-attach-file-without-creating-file

import javax.activation.DataHandler;
import javax.activation.DataSource;

try {
            // create a message
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress(from));
            InternetAddress[] address = {new InternetAddress(to)};
            msg.setRecipients(Message.RecipientType.TO, address);
            msg.setSubject(subject);

            // create and fill the first message part
            MimeBodyPart mbp1 = new MimeBodyPart();
            mbp1.setText(msgText1);

            // create the second message part
            MimeBodyPart mbp2 = new MimeBodyPart();

            // attach the file to the message
            **mbp2.attachFile(filename);**


            // create the Multipart and add its parts to it
            Multipart mp = new MimeMultipart();
            mp.addBodyPart(mbp1);
            mp.addBodyPart(mbp2);

            // add the Multipart to the message
            msg.setContent(mp);

            // set the Date: header
            msg.setSentDate(new Date());

            // send the message
            Transport.send(msg);

---

MimeBodyPart mbp = new MimeBodyPart();
String data = "any ASCII data";
DataSource ds = new ByteArrayDataSource(data, "application/x-any");
mbp.setDataHandler(new DataHandler(ds));

 

---

Sample 2:

MimeBodyPart attachmentPart = new MimeBodyPart();

try {
  DataSource ds = new ByteArrayDataSource(attachment.getBytes("UTF-8"), "application/octet-stream");
  attachmentPart = new MimeBodyPart();
  attachmentPart.setDataHandler(new DataHandler(ds));
} 
catch (Exception e) {
  Logger.getLogger("Blina").log(Level.SEVERE, Misc.getStackTrace(e));
}

attachmentPart.setFileName(fileName);
multipart.addBodyPart(attachmentPart);

// Put parts in message
msg.setContent(multipart);