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https://issues.apache.org/jira/browse/VFS-525?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16371497#comment-16371497
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Otto Fowler commented on VFS-525:
---------------------------------
For the size() changes : there is no way to 'clear' content once it is
retrieved. So once it is read it will not be read again. Even if you close,
the fileInfo is retrieved from the parent and it is cached and we get the size
from that
Not being able to invalidate the parent cache ( when you want to react to
external events ) is an issue here.
Maybe there needs to be an explicit 'Poll' api for this type of operation?
[~garydgregory]?
> 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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