Added in API level 26

FileVisitor

interface FileVisitor<T : Any!>

java.nio.file.FileVisitor

Known Direct Subclasses SimpleFileVisitor SimpleFileVisitor A simple visitor of files with default behavior to visit all files and to re-throw I/O errors.

A visitor of files. An implementation of this interface is provided to the java.nio.file.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;
              }
          });
  

Summary

Public methods
abstract FileVisitResult!	postVisitDirectory(dir: T, exc: IOException!) Invoked for a directory after entries in the directory, and all of their descendants, have been visited.
abstract FileVisitResult!	preVisitDirectory(dir: T, attrs: BasicFileAttributes!) Invoked for a directory before entries in the directory are visited.
abstract FileVisitResult!	visitFile(file: T, attrs: BasicFileAttributes!) Invoked for a file in a directory.
abstract FileVisitResult!	visitFileFailed(file: T, exc: IOException!) Invoked for a file that could not be visited.

Public methods

postVisitDirectory

Added in API level 26

abstract fun postVisitDirectory(
    dir: T, 
    exc: IOException!
): FileVisitResult!

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	T: a reference to the directory
exc	IOException!: 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

Return
FileVisitResult!	the visit result

Exceptions
java.io.IOException	if an I/O error occurs

preVisitDirectory

Added in API level 26

abstract fun preVisitDirectory(
    dir: T, 
    attrs: BasicFileAttributes!
): FileVisitResult!

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	T: a reference to the directory
attrs	BasicFileAttributes!: the directory's basic attributes

Return
FileVisitResult!	the visit result

Exceptions
java.io.IOException	if an I/O error occurs

visitFile

Added in API level 26

abstract fun visitFile(
    file: T, 
    attrs: BasicFileAttributes!
): FileVisitResult!

Invoked for a file in a directory.

Parameters
file	T: a reference to the file
attrs	BasicFileAttributes!: the file's basic attributes

Return
FileVisitResult!	the visit result

Exceptions
java.io.IOException	if an I/O error occurs

visitFileFailed

Added in API level 26

abstract fun visitFileFailed(
    file: T, 
    exc: IOException!
): FileVisitResult!

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	T: a reference to the file
exc	IOException!: the I/O exception that prevented the file from being visited

Return
FileVisitResult!	the visit result

Exceptions
java.io.IOException	if an I/O error occurs