IMAP - fetching the previous and next UIDs

Using standard spec IMAP 开发者_C百科commands, how can I determine the previous and next UIDs in a mailbox based on a passed UID, sorting the mailbox messages by date, newest first?

I have found new mail UID with below code.

   @Override
        public void messagesAdded(MessageCountEvent e) {
         try {
             long newMailUID = ((IMAPFolder) e.getSource()).getUIDNext()
         } catch (MessagingException e1) {
             e1.printStackTrace();
         }
       }

Assuming that "sorting the mailbox messages by date, newest first" refers to the time the messages were added to the mailbox rather than INTERNALDATE or the Date header:

A001 SEARCH UID 82342
* SEARCH 83
A001 OK SEARCH completed

A002 FETCH 82,84 UID
* FETCH 82 (UID 82309)
* FETCH 84 (UID 82343)
A002 OK FETCH completed

Things to look out for:

• If the UID doesn't exist in the mailbox, SEARCH will return no results.
• If the UID matched the first/last message in the mailbox, don't try to fetch the one before/after or you'll get a BAD response.

If you'd prefer not to use SEARCH, you could also do the UID-to-sequence via UID FETCH:

A001 UID FETCH 82342 UID
* FETCH 83 (UID 82342)
A001 OK UID FETCH completed

I think the only way would be to ask for all UIDs first:

UID SEARCH ALL

...and sort. Each message added to the mailbox is assigned a higher UID than the messages which were added previously.

So higher UID = newer email.

If you want to search for the UID before 12345, this command will do it:

a UID SEARCH RETURN (MAX) UID 1:12344

Finding the next after:

b UID SEARCH RETURN (MIN) UID 12346:*

This requires the ESEARCH extension, which most modern servers implement. Notably gmail implements it. It's a little too expensive to issue in a loop, though, so perhaps you're better off solving your issue in another way. Here's a two-command sequence to get the 50 UIDs immediately preceding 12345:

c1 SEARCH UID 12345
* SEARCH 1000
c1 OK done
c2 UID SEARCH 950:999
* SEARCH 12200,12202,...
c2 OK done

950 is "result of c1 - 50", 999 is "result of c1 - 1".

I'm not familiar with the exact commands, but have you checked out the RFC?

https://www.rfc-editor.org/rfc/rfc3501

Looks like there is a UIDNEXT command you can send that gives you the next UID.