Odd result with canonical paths with intermixed usage of java.io.File and java.nio.file.Files APIs

[Jaikiran Pai]

Moved this thread from discussions mailing list[1] to here. Comments inline.


On 11/12/17 7:55 PM, Alan Bateman wrote:
> On 11/12/2017 14:06, Jaikiran Pai wrote:
>> :
>>
>> So a few related questions that I have are:
>>
>>     1. Is this inconsistency an expected behaviour or is this a bug?
>>     2. If this is an expected behaviour, then would it be a better 
>> idea (as an application developer) to use Path.toRealPath[2] instead 
>> of using the File.getCanonicalPath()? Are these 2 APIs semantically 
>> equivalent? The File.getCanonicalPath() talks about the canonical 
>> path being "unique" paths but the Path.toRealPath has no such mentions.
>>
> The correctness issues with the canonicalization cache is a long 
> standing issue [1]. You can workaround it by running with 
> -Dsun.io.useCanonCaches=false as I think you have found. The goal is 
> to eventually disable and remove it. The first steps to get there 
> happened in JDK 9 when FilePermission was changed to not canonicalize 
> by default (FilePermission was the original motivation for this cache).
>
> If you have follow-up questions then please bring the thread to 
> core-libs-dev.
>
> -Alan
>
> [1] https://bugs.openjdk.java.net/browse/JDK-7066948
Thanks Alan. Given that the cache itself is being planned to be 
eventually removed, that answers the main part of my question and I can 
workaround this issue in a couple of ways (disabling the cache using 
that system property is one way) in the application, till that time.

The only remaining part that I'm curious about is this:

 > ... would it be a better idea (as an application developer) to use 
Path.toRealPath[2] instead of using the File.getCanonicalPath()? Are 
these 2 APIs semantically equivalent? The File.getCanonicalPath() talks 
about the canonical path being "unique" paths but the Path.toRealPath 
has no such mentions.


[1] http://mail.openjdk.java.net/pipermail/discuss/2017-December/004655.html


-Jaikiran