RFR: 8283335 : Add exists and readAttributesIfExists methods to FileSystemProvider

[Brian Burkhalter]

On Wed, 22 Jun 2022 19:05:41 GMT, Lance Andersen <lancea at openjdk.org> wrote:

> Hi,
> 
> Please review the following patch which will:
> 
> - Enhance the java.nio.file.spi.FileSystemProvider abstract class to include the methods
> 
>   - public boolean exists(Path path, LinkOption... options)
>   - public <A extends BasicFileAttributes> A readAttributesIfExists(Path path, Class<A> type, LinkOption... options)
> 
> 
> This change allows for providers to provide optimizations when the file's attributes are not needed.
> 
> Mach5 tiers 1 - 3  run clean with this change
> 
> The CSR may be viewed at [JDK-8283336](https://bugs.openjdk.org/browse/JDK-8283336)
> 
> 
> Best,
> Lance

src/java.base/unix/classes/sun/nio/fs/UnixFileAttributes.java line 80:

> 78:     static UnixFileAttributes getIfExists(UnixPath path) throws UnixException {
> 79:         UnixFileAttributes attrs = new UnixFileAttributes();
> 80:         int errno = UnixNativeDispatcher.stat2(path, attrs);

I think that this is the only use of `stat2()`. It could be deleted if this method were replaced with this:


    static UnixFileAttributes getIfExists(UnixPath path) throws UnixException {
        UnixFileAttributes attrs = new UnixFileAttributes();
        try {
            UnixNativeDispatcher.stat(path, attrs);
            return attrs;
        } catch (UnixException e) {
            if (e.errno() == UnixConstants.ENOENT) {
                return null;
            }
            throw e;
        }
    }

-------------

PR: https://git.openjdk.org/jdk/pull/9249