RFR: 8057113: (fs) Path should have a method to obtain the filename extension

[Remi Forax]

----- Mail original -----
> De: "Brian Burkhalter" <bpb at openjdk.java.net>
> À: "nio-dev" <nio-dev at openjdk.java.net>
> Envoyé: Vendredi 29 Janvier 2021 22:32:52
> Objet: RFR: 8057113: (fs) Path should have a method to obtain the filename extension

> Please review this proposed change to add a method
> `java.nio.file.Path.getExtension()`. This was initially discussed in the thread
> http://mail.openjdk.java.net/pipermail/nio-dev/2018-February/004716.html. This
> method would return the filename extension of the file name of the `Path`. The
> extension is defined to be the portion of the file name after the last dot
> `(‘.’)`.
> 
> The definitions of file extension for about fifteen platforms and languages were
> surveyed to try to find a reasonable compromise for the definition of
> extension. The most common definition was the last segment of the name
> including and after the last dot. The second definition omitted the last dot
> from the extension. Java-related platforms all exclude the last dot. (One
> divergent definition in the internal Java NIO method
> `AbstractFileTypeDetector.getExtension(String)` defines the extension as the
> part after the *first* dot.)
> 
> All examined cases define the extension to be an empty string if it cannot be
> determined. None of these cases used `null` to represent an indeterminate
> extension.
> 
> Little in the way of specifying behavior for special cases (consisting mainly of
> file names with one or more leading dots) was found. Most definitions concern
> themselves only with the last dot and what comes after it and ignore leading
> dots altogether. A few definitions ignore a leading dot at the zeroth
> character. The current proposal ignores a dot at character zero.
> 
> The behavior of the proposed method for some example cases is as:
> 
> .              ->
> ..             ->
> .a.b           -> b
> ......         ->
> .....a         -> a
> ....a.b        -> b
> ..foo          -> foo
> test.rb        -> rb
> a/b/d/test.rb  -> rb
> .a/b/d/test.rb -> rb
> foo.           ->
> test           ->
> .profile       ->
> .profile.sh    -> sh
> ..foo          -> foo
> .....foo       -> foo
> .vimrc         ->
> test.          ->
> test..         ->
> test...        ->
> image.jpg      -> jpg
> music.mp3      -> mp3
> video.mp4      -> mp4
> document.txt   -> txt
> 
> If the specification can be agreed upon, then a test will be added to this PR
> and a corresponding CSR will be filed.

Thanks for doing this !

Usually in JDK codes, the return value is returned early instead of being stored in a local variable and then returned.
So a code like below is more usual.

   default String getExtension() {
        String name = getFileName().toString();
        int length = name.length();

        // Indeterminate if name is too short or equal to "..".
        if (length > 1 && !name.equals("..")) {
            int lastDotIndex = name.lastIndexOf('.');
            // Indeterminate if no dot or found at last or only the first index
            if (lastDotIndex > 0 && lastDotIndex < length - 1) {
                return name.substring(lastDotIndex + 1);
            }
        }
        return "";
    }

regards,
Rémi

> 
> -------------
> 
> Commit messages:
> - 8057113: (fs) Path should have a method to obtain the filename extension
> 
> Changes: https://git.openjdk.java.net/jdk/pull/2319/files
> Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2319&range=00
>  Issue: https://bugs.openjdk.java.net/browse/JDK-8057113
>  Stats: 37 lines in 1 file changed: 36 ins; 0 del; 1 mod
>  Patch: https://git.openjdk.java.net/jdk/pull/2319.diff
>  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2319/head:pull/2319
> 
> PR: https://git.openjdk.java.net/jdk/pull/2319