Java Reference
In-Depth Information
METHOD
DESCRIPTION
This is called immediately before the entries in the directory
dir
are visited. The second argu-
ment is the directory's basic attributes. This method provides you with the means of con-
trolling what happens next. You should return one of the following constants defined by the
FileVisitResult
enum that is in the
java.nio.file
package.
CONTINUE
: Entries in
dir
are
visited.
SKIP_SIBLINGS
or
SKIP_SUBTREE
: Entries in
dir
and any subdirectories will not be
visited.
preVisitDirectory(
Path dir,
BasicFileAttributes
attr)
This is called after entries in the
dir
directory and their descendants have been visited. This
method is also called when visiting entries in the directory is terminated by the
visitFile()
method returning
SKIP_SIBLINGS
or an I/O error occurs. If an I/O error occurs while entries
are being visited,
e
references the exception object that was thrown. Otherwise
e
is
null
.
postVisitDirectory(
Path dir, IOExcep-
tion e)
This is called when the
file
file is visited. The
attr
parameter references the attributes for
the file.
visitFile( Path
file, BasicFileAt-
tributes attr)
This is called when the attributes for
file
cannot be read or the directory containing the file
cannot be opened.
e
references the exception object thrown as a result of an I/O error.
visitFileFailed(
Path file, IOExcep-
tion e)
There are two versions of the static
walkFileTree()
method. The simplest accepts two arguments:
• A
Path
object specifying the starting directory for the tree to be walked.
• A reference to a
FileVisitor
object that implements the methods mentioned earlier to do what
you want with the files and directories in the tree.
This version of the method does not follow links and visits all levels in the file tree. The other version of
walkFileTree()
accepts four arguments:
• The starting directory path, as before.
• A set of
java.nio.file.FileVisitOption
enumeration constants, that contains either
FOLLOW_LINKS
supplied in an
EnumSet
or an empty
EnumSet
. Specifying
FOLLOW_LINKS
causes
file links to be followed.
• A value of type
int
specifies the maximum depth to be explored in the file tree.
• The
FileVisitor
object that implements the methods that are called in the process of walking the
file tree.
The class
java.util.EnumSet
defines an object that can store a set of enumeration constants. You learn
more about the
EnumSet
class in Chapter 14 so just take it for granted for the moment. To specify an
EnumSet
containing
FOLLOW_LINKS
you can use the expression
EnumSet.of(FOLLOW_LINKS)
. To define
an empty
EnumSet
of
FileVisitOption
constants you use the expression
EnumSet.noneOf(FileVisitOption.class)
. The expressions assume that you have imported the con-
stants from the enumeration and you have an import statement for
EnumSet
.
The process for walking a file tree may seem a little hazy at this point, but an example should clarify it.
TRY IT OUT: Walking a File Tree
First I will define a class that implements the
FileVisitor<Path>
interface:
