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From "Volker Bergmann (JIRA)" <j...@apache.org>
Subject [jira] [Created] (VFS-525) FtpFileObject.exists() output not impacted by refresh() after file deletion
Date Sat, 10 May 2014 22:06:41 GMT
Volker Bergmann created VFS-525:
-----------------------------------

             Summary: 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


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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