Input and Output - Java 8 Recipes - page 303

How It Works
Before NIO.2, trying to traverse a directory tree involved recursion, and depending on
the implementation, it could be very brittle. The calls to get files within a folder were
synchronous and required the scanning of the whole directory before returning; gener-
ating what would appear to be an unresponsive method call to an application user. With
the new NIO.2, one can specify which folder to start traversing on, and the NIO.2 calls
will handle the recursion details. The only item that you provide to the NIO.2 API is a
class that tells it what to do when a file/folder is found ( SimpleFileVisitor im-
plementation). NIO.2 uses a Visitor pattern, so it isn't required to prescan the entire
folder, but instead processes files as they are being iterated over.
The implementation of the SimpleFileVisitor class as an anonymous inner
class includes overriding the visitFile(Path file, BasicFileAttrib-
utesattrs() method. When you override this method, you can specify the tasks to
perform when a file is encountered.
The visitFile method returns a FileVisitReturn enum. This enum then
tells the FileVisitor which action to take:
• CONTINUE : Continues with the traversing of the directory tree.
• TERMINATE : Stops the traversing.
• SKIP_SUBTREE : Stops going deeper from the current tree level (use-
ful only if this enum is returned on the preVisitDirectory()
method).
• SKIP_SIBLINGS : Skips the other directories at the same tree level as
the current.
The SimpleFileVisitor class, aside from the visitFile() method, also
contains the following:
• preVisitDirectory : Called before entering a directory to be tra-
versed.
• postVisitDirectory : Called after finished traversing a directory.
• visitFile : Called as it visits the file, as in the example code.
• visitFileFailed : Called if the file cannot be visited; for example,
on an I/O error.