Strategy for scanning directories. Implementations may select all children
and grandchildren of the scanned directory in any order. This interface is
intended to enable the customization of selection, locking and ordering of
files in a directory like RecursiveDirectoryScanner. If the only requirement
is to ignore certain files a EntryListFilter implementation should suffice.
Sets a custom filter to be used by this scanner. The filter will get a
chance to reject files before the scanner presents them through its
listFiles method. A scanner may use additional filtering that is out of
the control of the provided filter.
Claim the file to process. It is up to the implementation to decide what
additional safe guards are required to attain a claim to the file. But if
a locker is set implementations MUST invoke its lock method
and MUST return false if the locker did not grant the lock.