javamail 下载附件

您可以使用JavaMail库来下载电子邮件附件。以下是一个简单的示例代码，演示了如何从电子邮件中下载附件：

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

import javax.mail.BodyPart;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.Part;
import javax.mail.Session;
import javax.mail.Store;

public class EmailAttachmentDownloader {

    public static void main(String[] args) {
        String host = "your_email_host";
        String username = "your_email_username";
        String password = "your_email_password";
        int messageNumber = 1; // 要下载附件的电子邮件的序号
        String saveDirectory = "path_to_save_attachments"; // 附件保存的目录

        Properties properties = new Properties();
        properties.put("mail.store.protocol", "pop3");
        properties.put("mail.pop3.host", host);
        properties.put("mail.pop3.port", "995");
        properties.put("mail.pop3.ssl.enable", "true");

        Session session = Session.getDefaultInstance(properties);

        try {
            Store store = session.getStore("pop3s");
            store.connect(host, username, password);

            Folder emailFolder = store.getFolder("INBOX");
            emailFolder.open(Folder.READ_ONLY);

            Message message = emailFolder.getMessage(messageNumber);

            Multipart multipart = (Multipart) message.getContent();

            for (int i = 0; i < multipart.getCount(); i++) {
                BodyPart bodyPart = multipart.getBodyPart(i);
                if (Part.ATTACHMENT.equalsIgnoreCase(bodyPart.getDisposition())) {
                    String fileName = bodyPart.getFileName();
                    InputStream inputStream = bodyPart.getInputStream();
                    FileOutputStream outputStream = new FileOutputStream(new File(saveDirectory + File.separator + fileName));

                    byte[] buffer = new byte[4096];
                    int bytesRead;
                    while ((bytesRead = inputStream.read(buffer)) != -1) {
                        outputStream.write(buffer, 0, bytesRead);
                    }

                    outputStream.close();
                    inputStream.close();
                }
            }

            emailFolder.close(false);
            store.close();
        } catch (MessagingException | IOException e) {
            e.printStackTrace();
        }
    }
}

请确保将`your_email_host`，`your_email_username`，`your_email_password`和`path_to_save_attachments`替换为实际的值。此示例代码假设您正在使用POP3协议。

这段代码将连接到指定的电子邮件服务器，打开收件箱文件夹，获取指定序号的电子邮件，并将其中的附件保存到指定目录中。

请注意，该示例代码只适用于下载单个附件。如果电子邮件中有多个附件，您可能需要根据需要进行修改，以处理所有附件。