How to reach previously read emails by using Spring Integration?

Question

I am developing a dynamic and multiple IMAP channel listener application. For the purpose of effectiveness, I am not downloading the attachments inside mails, just getting the texts inside them. Also I am developing an endpoint to access that previously arrived mails and download & return that attachment in order not to download every attachment. So basically I am trying to download attachments only if there is a demand.

I am using ImapIdleChannelAdapter to listen mails inside integration flow. Here is my flow,

public ImapIdleChannelAdapter mailAdapter(ImapMailReceiver receiver) {
        ImapIdleChannelAdapter imapAdapter = new ImapIdleChannelAdapter(receiver);
        imapAdapter.setAutoStartup(true);
        return imapAdapter;
    }

public IntegrationFlow createMailFlow(GmailRecieverRequirements requirements, String clientID) {
        return IntegrationFlow.from(
                mailAdapter(gmailMailReceiver(requirements)))
                .handle(getMailHandler())
                .get();
    }

My question is, how can I access those previously read mails in different time? I know Java Mail has Folder - UID structure to access mails via UIDs. Here is the link . However, I do not want to use javaMail inside my flow to save the UID. Is there any chance that I could reach UID of the mail inside the flow by Spring Integration? I am open to any other solution.

Thanks in advance

Answer 1

This is indeed low-level mail API functionality. Not sure what you mean with your do not want to use javaMail inside my flow , but we only can do that on demand fetching if we know the folder and message UID and with that respective API of the IMAPFolder :

/**
 * Get the Message corresponding to the given UID. If no such 
 * message exists, <code>null</code> is returned.
 *
 * @param uid   UID for the desired message
 * @return      the Message object. <code>null</code> is returned
 *          if no message corresponding to this UID is obtained.
 * @exception   MessagingException for failures
 */
public Message getMessageByUID(long uid) throws MessagingException;

The ImapIdleChannelAdapter can produce raw jakarta.mail.Message to let you to obtain its UID via UIDFolder.getUID(Message message) API.