RFR: 8298318: (fs) APIs for handling filename extensions [v2]

[Anthony Vanelverdinghe]

On Mon, 27 Nov 2023 16:59:34 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Two popular Java libraries for file access and path utilities are Apache Commons and Guava,
> both do not consider the "." to be part of the extension.

Point taken, it would be confusing if the JDK would behave otherwise, though only for Java developers who are actually accustomed to the methods in those libraries. Given how easy it is to just do `filename.substring(filename.lastIndexOf('.'))`, I'd argue that there's at least as many Java developers who would expect the dot to be part of the extension.

> They also do not consider a leading "." to be a delimiter of an extension.

This is factually false: both [Guava](https://guava.dev/releases/32.1.3-jre/api/docs/com/google/common/io/MoreFiles.html#getFileExtension(java.nio.file.Path)) and [Apache Commons](https://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/FilenameUtils.html#getExtension(java.lang.String)) consider a leading dot to be a delimiter of an extension, both in their Javadoc specification and in their implementation:

![image](https://github.com/openjdk/jdk/assets/15714253/dfb92224-d871-4b70-8fec-675e93264de4)

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PR Comment: https://git.openjdk.org/jdk/pull/16226#issuecomment-1828339847