Otto Fowler updated VFS-525:
    Comment: was deleted

(was: I think more properly the question is where *DOES* VFS _ever_ detect 
external changes?


> FtpFileObject.exists() output not impacted by refresh() after file deletion
> ---------------------------------------------------------------------------
>                 Key: VFS-525
>                 URL: https://issues.apache.org/jira/browse/VFS-525
>             Project: Commons VFS
>          Issue Type: Bug
>    Affects Versions: 2.0
>         Environment: Windows 7 [Version 6.1.7601]
> java version "1.6.0_31"
> Java(TM) SE Runtime Environment (build 1.6.0_31-b05)
> Java HotSpot(TM) Client VM (build 20.6-b01, mixed mode, sharing)
> commonc vfs 2.0
> commons net 3.3
>            Reporter: Volker Bergmann
>            Priority: Critical
>              Labels: FTP,, cache, exists
> Context: I store a file in an FTP directory and poll the FTP file (using 
> FtpFileObject.exists()) until it is imported by another system and deleted on 
> the FTP folder.
> Issue: On the first lookup, the file is present and FtpFileObject.exists() 
> returns true correctly. That's OK, but after the file has been deleted, 
> FtpFileObject.exists() continues to return true, even when using 
> CacheStrategy.MANUAL and calling FtpFileObject.refresh().
> Observations: Upon refresh() there is a complex interaction between the file 
> and parent folder object as well as the code of AbstractFileObject and 
> FtpFileObject. The issue seems to stem from the fact that for the existence 
> check of a file, its parent file object is queried for its #children 
> attribute which caches the child entries. On the one hand, the child file 
> seems to clear the link to the parent folder, causing a detach() of the 
> parent, but since the parent folder already is in detached state, it does not 
> clear its #children attribute. 
> By the way: I consider it a poor inheritance design if a child class 
> attribute 
>     FtpFileObject: private Map<String, FTPFile> children
> shadows a parent class attribute
>     AbstractFileObject: private FileName[] children
> At least it makes debugging more cumbersome.
> Workaround: The issue stems from the fact that the parent FtpFileObject is 
> not cleared correctly because attached==false. Thus I use a call to the 
> parent's getType() method which causes an attach() and, finally, attached== 
> true and then call refresh() on the parent and the child:
> // This is a workaround for VFS 2.0's flaws in the 
> // handling of attached/detached state and caching:
> FileObject parent = file.getParent();
> parent.getType(); // assure that parent folder is attached
> parent.refresh(); // detach parent folder and clear child object cache 
>                         // (works only if attached before)
> // ...end of workaround
> file.refresh();
> System.out.println("File.exists(): {}", file.exists());

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