通过JavaMail使用POP3获取电子邮件的接收日期出现问题

Question

我正在尝试通过javamail获取yahoo.de的电子邮件信息。我已经获取了主题，发件人，收件人等信息，但是我无法获取电子邮件的接收日期。我使用了getReceivedDate方法，但它返回null。以下是我的代码...请问有谁能帮助我如何通过javamail和POP3获取电子邮件的接收日期？

import java.io.IOException;
import java.util.Properties;
import javax.mail.Flags;
import javax.mail.Folder;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Store;

public class FolderFetchPop3 {

    public static void main(String[] args) throws MessagingException, IOException {
        Folder folder = null;
        Store store = null;

        try {
            Properties props = System.getProperties();
            props.setProperty("mail.store.protocol", "pop3");
            Session session = Session.getDefaultInstance(props, null);
            store = session.getStore("pop3");
            store.connect("pop.mail.yahoo.com","[e-mail]", "password of emailid");
            folder = store.getFolder("inbox");

            if(!folder.isOpen())
            folder.open(Folder.READ_WRITE);
            Message[] messages = folder.getMessages();
            System.out.println("No of Messages : " + folder.getMessageCount());
            System.out.println("No of Unread Messages : " + folder.getUnreadMessageCount());
            System.out.println(messages.length);
            for (int i=0; i < messages.length;i++) {
                System.out.println("*****************************************************************************");
                System.out.println("MESSAGE " + (i + 1) + ":");
                Message msg =  messages[i];
                //System.out.println(msg.getMessageNumber());
                System.out.println("Subject: " + msg.getSubject());
                System.out.println("From: " + msg.getFrom()[0]);
                System.out.println("To: "+msg.getAllRecipients()[0]);
                System.out.println("Date: "+msg.getReceivedDate());
                System.out.println("Size: "+msg.getSize());
            }
        } finally {
            if (folder != null && folder.isOpen()) { folder.close(true); }
            if (store != null) { store.close(); }
        }
    }
}

- user523956

Answer 1

请查看Java Mail API FAQ：

问：为什么使用POP3时，getReceivedDate()返回null？
答：POP3协议不提供有关收到消息的时间信息。通过查看一些消息头（例如“Received”头），可能可以猜测接收日期，但这不是非常可靠的。

因此，为了获取有关接收日期的一些信息，请查看MimeMessage#getHeader(String name)并尝试获取您可以尝试解释的Received头。

- dertkw

---

有什么想法为什么它不可靠，以及期望多高的可靠性水平？ - Ciaran Gallagher

@CiaranGallagher 可靠性的程度取决于设置“Received”头的工具/应用程序/服务器。如果没有设置，显然无法使用它。 - dertkw

Answer 2

我已经准备好了这个简单的“接收日期解析器”，可以从接收头中获取最新的日期。

public static final String RECEIVED_HEADER_DATE_FORMAT = "EEE, d MMM yyyy HH:mm:ss Z";
public static final String RECEIVED_HEADER_REGEXP = "^[^;]+;(.+)$";

public Date resolveReceivedDate(MimeMessage message) throws MessagingException {
    if (message.getReceivedDate() != null) {
        return message.getReceivedDate();
    }
    String[] receivedHeaders = message.getHeader("Received");
    if (receivedHeaders == null) {
        return (Calendar.getInstance().getTime());
    }
    SimpleDateFormat sdf = new SimpleDateFormat(RECEIVED_HEADER_DATE_FORMAT);
    Date finalDate = Calendar.getInstance().getTime();
    finalDate.setTime(0l);
    boolean found = false;
    for (String receivedHeader : receivedHeaders) {
        Pattern pattern = Pattern.compile(RECEIVED_HEADER_REGEXP);
        Matcher matcher = pattern.matcher(receivedHeader);
        if (matcher.matches()) {
            String regexpMatch = matcher.group(1);
            if (regexpMatch != null) {
                regexpMatch = regexpMatch.trim();
                try {
                    Date parsedDate = sdf.parse(regexpMatch);
                    LogMF.debug(log, "Parsed received date {0}", parsedDate);
                    if (parsedDate.after(finalDate)) {
                        //finding the first date mentioned in received header
                        finalDate = parsedDate;
                        found = true;
                    }
                } catch (ParseException e) {
                    LogMF.warn(log, "Unable to parse date string {0}", regexpMatch);
                }
            } else {
                LogMF.warn(log, "Unable to match received date in header string {0}", receivedHeader);
            }
        }
    }

    return found ? finalDate : Calendar.getInstance().getTime();
}

希望这有所帮助。如果您有任何改进意见，请让我知道。

彼得

- shimon001