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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IO-271) FileUtils.copyDirectory should be able to handle arbitrary number of files
Date Sat, 07 May 2011 14:08:03 GMT

    [ https://issues.apache.org/jira/browse/IO-271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030354#comment-13030354
] 

Sebb commented on IO-271:
-------------------------

If using String[] list() instead of File[] listFile():
* when using a filter, each String has to be turned into a File.
* the copy stage also requires the String to be turned into a File.

Using String[] does reduce the maximum memory requirements as the File lifetime is very short.
However in the filtered case it can double the number of File instances that need to be created.

Also, the listFiles() methods are more efficient, because they take advantage of the fact
that the list() entries have already been normalised.

I'm not sure these trade-offs are worth it for the general case.

> FileUtils.copyDirectory should be able to handle arbitrary number of files
> --------------------------------------------------------------------------
>
>                 Key: IO-271
>                 URL: https://issues.apache.org/jira/browse/IO-271
>             Project: Commons IO
>          Issue Type: Improvement
>          Components: Utilities
>    Affects Versions: 2.0.1
>            Reporter: Stephen Kestle
>            Priority: Minor
>
> File.listFiles() uses up to a bit over 2 times as much memory as File.list().  The latter
should be used in doCopyDirectory where there is no filter specified.
> This memory usage is a problem when copying directories with hundreds of thousands of
files.
> I was also thinking of the option of implementing a file filter (that could be composed
with the inputted filter) that would batch the file copy operation; copy the first 10000 (that
match), then the next 10000 etc etc.
> Because of the lack of ordering consistency (between runs) of File.listFiles(), there
would need to be a final file filter that would accept files that have not successfully been
copied.
> I'm primarily concerned about copying into an empty directory (I validate this beforehand),
but for general operation where it's a merge, the modification date re-writing should only
be done in the final run of copies so that while batching occurs (and indeed the final "missed"
filtering) files do not get copied if they have been modified after the start time. (I presume
that I'm reading FileUtils correctly in that it overrides files...)

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