[jira] [Commented] (VFS-525) FtpFileObject.exists() output not impacted by refresh() after file deletion

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[jira] [Commented] (VFS-525) FtpFileObject.exists() output not impacted by refresh() after file deletion

JIRA jira@apache.org

    [ https://issues.apache.org/jira/browse/VFS-525?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16375002#comment-16375002 ]

Otto Fowler commented on VFS-525:

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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