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Interface FileVisitor<T>

Type Parameters:: T - the type of file/directory

All Known Implementing Classes:: SimpleFileVisitor

public interface FileVisitor<T>

A visitor of files. An implementation of this interface is provided to the Files.walkFileTree methods to visit each file in a file tree.

Usage Examples: Suppose we want to delete a file tree. In that case, each directory should be deleted after the entries in the directory are deleted.

    Path start = ...
    Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
            throws IOException
        {
            Files.delete(file);
            return FileVisitResult.CONTINUE;
        }
        @Override
        public FileVisitResult postVisitDirectory(Path dir, IOException e)
            throws IOException
        {
            if (e == null) {
                Files.delete(dir);
                return FileVisitResult.CONTINUE;
            } else {
                // directory iteration failed
                throw e;
            }
        }
    });

Furthermore, suppose we want to copy a file tree to a target location. In that case, symbolic links should be followed and the target directory should be created before the entries in the directory are copied.

    final Path source = ...
    final Path target = ...

    Files.walkFileTree(source, EnumSet.of(FileVisitOption.FOLLOW_LINKS), Integer.MAX_VALUE,
        new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                throws IOException
            {
                Path targetdir = target.resolve(source.relativize(dir));
                try {
                    Files.copy(dir, targetdir);
                } catch (FileAlreadyExistsException e) {
                     if (!Files.isDirectory(targetdir))
                         throw e;
                }
                return CONTINUE;
            }
            @Override
            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
                throws IOException
            {
                Files.copy(file, target.resolve(source.relativize(file)));
                return CONTINUE;
            }
        });

Since:: 1.7

Method Summary

Modifier and Type	Method	Description
`FileVisitResult`	`postVisitDirectory(T dir, IOException exc)`	Invoked for a directory after entries in the directory, and all of their descendants, have been visited.
`FileVisitResult`	`preVisitDirectory(T dir, BasicFileAttributes attrs)`	Invoked for a directory before entries in the directory are visited.
`FileVisitResult`	`visitFile(T file, BasicFileAttributes attrs)`	Invoked for a file in a directory.
`FileVisitResult`	`visitFileFailed(T file, IOException exc)`	Invoked for a file that could not be visited.

Method Details

preVisitDirectory

FileVisitResult preVisitDirectory(T dir, BasicFileAttributes attrs) throws IOException

Invoked for a directory before entries in the directory are visited.

If this method returns CONTINUE, then entries in the directory are visited. If this method returns SKIP_SUBTREE or SKIP_SIBLINGS then entries in the directory (and any descendants) will not be visited.

Parameters:: dir - a reference to the directory; attrs - the directory's basic attributes
Returns:: the visit result
Throws:: IOException - if an I/O error occurs

visitFile

FileVisitResult visitFile(T file, BasicFileAttributes attrs) throws IOException

Invoked for a file in a directory.

Parameters:: file - a reference to the file; attrs - the file's basic attributes
Returns:: the visit result
Throws:: IOException - if an I/O error occurs

visitFileFailed

FileVisitResult visitFileFailed(T file, IOException exc) throws IOException

Invoked for a file that could not be visited. This method is invoked if the file's attributes could not be read, the file is a directory that could not be opened, and other reasons.

Parameters:: file - a reference to the file; exc - the I/O exception that prevented the file from being visited
Returns:: the visit result
Throws:: IOException - if an I/O error occurs

postVisitDirectory

FileVisitResult postVisitDirectory(T dir, IOException exc) throws IOException

Invoked for a directory after entries in the directory, and all of their descendants, have been visited. This method is also invoked when iteration of the directory completes prematurely (by a visitFile method returning SKIP_SIBLINGS, or an I/O error when iterating over the directory).

Parameters:: dir - a reference to the directory; exc - null if the iteration of the directory completes without an error; otherwise the I/O exception that caused the iteration of the directory to complete prematurely
Returns:: the visit result
Throws:: IOException - if an I/O error occurs

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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/nio/file/FileVisitor.html