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From "Feeling Groovy (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (IO-340) The use of file.exists() is failure prone. Where file.exists() is checked, it should be replaced with the following dual check: exists = ( file.exists() || file.length()>0 )
Date Sat, 13 Oct 2012 12:28:03 GMT

     [ https://issues.apache.org/jira/browse/IO-340?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Feeling Groovy updated IO-340:
------------------------------

    Comment: was deleted

(was: Repeats calls to file.exists() does nothingto remedy the false values. From my own experience
on various java versions, on Windows XP and 7 (32 and 64), is that when file.exists() is wrong,
that file.length() does in fact report a non-zero length and correctly report then that the
file does in fact exist.

I found this bug when I was reading and renaming many files and the File object started providing
false exists() values. Like I said, for some reason, file.exists || file.length()>0 works
for me 100% of the time where exists() failed.

I might suggest not using those file.exists() check and instead construct the FileInputStream
early to catch any FileNotFound error ( to indicate that it does not exist). Then, the same
stream can be used for the actual file comparison in routines like the contentsEquals functions.

)
    
> The use of file.exists() is failure prone. Where file.exists() is checked, it should
be replaced with the following dual check:  exists = ( file.exists() || file.length()>0
)
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: IO-340
>                 URL: https://issues.apache.org/jira/browse/IO-340
>             Project: Commons IO
>          Issue Type: Bug
>          Components: Utilities
>    Affects Versions: 2.5, 3.x
>         Environment: All
>            Reporter: Feeling Groovy
>              Labels: File, exists, false
>             Fix For: 2.5, 3.x
>
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> The use of file.exists() is failure prone. In many cases the jvm can report that a file
does not exist even when it does. This is due to the caching in the operating system.
> Since file.exists() is prone to report false values, a second check can and should be
made to file.length()>0.
> Where file.exists() is checked, it should be replaced with the following dual check:
 
> A file more reliably exists if:  file.exists() || file.length()>0
> Then if the file does not exist, file.length will be 0.

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