WatchService / detecting renames and moves

[Alan Bateman]

On 09/01/2012 19:56, Johannes.Lichtenberger wrote:
> Hello,
>
> I'm using a WatchService to monitor changes in a directory recursively.
> Now I want to add a simple rename or move-detection. Therefore I
> probably can use java.nio.file.attribute.BasicFileAttributes.fileKey()
> but I think the order in which I receive events isn't specified (CREATE
> =>  DELETE, DELETE =>  CREATE) or is it also possible to get other CREATE
> / DELETE events between the events originating from a move or
> rename-operation? That would for sure complicate the situation, but I
> think that's possible because I haven't read anything which guarantees
> any order. Furthermore the fileKeys can be reused by the Filesystem,
> which is also why I'm questioning my approach. Maybe using hashes and
> the fileKeys... but I don't want to save a new queue of events, which
> would be a heuristic, because after some time no equal fileKey + hash is
> encountered I would suggest they are "real" DELETE/CREATE-events. Maybe
> I should simply switch to JPathWatch as it should definately work on
> Linux and optionally on Windows, which both seem to support and "export"
> move-events)?
>
> kind regards,
> Johannes
Rename or move-in/out events aren't strictly required as the CREATE and 
DELETE events should allow you to keep your view of the directory up to 
the date. The reason that these events weren't included originally is 
because out of concern that they would not be feasible with all 
implementations and also the concern as to how such events would be 
linked when renaming between directories.  That said, it is something 
that we should come back to. As regards the fileKey() method then in 
theory it could be recycled quickly although in practice it should do 
what you want on the platforms where fileKey() returns non-null.

-Alan