/*
* Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.nio.file;
import java.nio.file.attribute.BasicFileAttributes;
import java.io.IOException;
/**
* A visitor of files. An implementation of this interface is provided to the
* {@link Files#walkFileTree Files.walkFileTree} methods to visit each file in
* a file tree.
*
* <p> <b>Usage Examples:</b>
* Suppose we want to delete a file tree. In that case, each directory should
* be deleted after the entries in the directory are deleted.
* <pre>
* 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;
* }
* }
* });
* </pre>
* <p> 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.
* <pre>
* 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;
* }
* });
* </pre>
*
* @since 1.7
*/
public interface FileVisitor<T> {
/**
* Invoked for a directory before entries in the directory are visited.
*
* <p> If this method returns {@link FileVisitResult#CONTINUE CONTINUE},
* then entries in the directory are visited. If this method returns {@link
* FileVisitResult#SKIP_SUBTREE SKIP_SUBTREE} or {@link
* FileVisitResult#SKIP_SIBLINGS SKIP_SIBLINGS} then entries in the
* directory (and any descendants) will not be visited.
*
* @param dir
* a reference to the directory
* @param attrs
* the directory's basic attributes
*
* @return the visit result
*
* @throws IOException
* if an I/O error occurs
*/
FileVisitResult preVisitDirectory(T dir, BasicFileAttributes attrs)
throws IOException;
/**
* Invoked for a file in a directory.
*
* @param file
* a reference to the file
* @param attrs
* the file's basic attributes
*
* @return the visit result
*
* @throws IOException
* if an I/O error occurs
*/
FileVisitResult visitFile(T file, BasicFileAttributes attrs)
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.
*
* @param file
* a reference to the file
* @param exc
* the I/O exception that prevented the file from being visited
*
* @return the visit result
*
* @throws IOException
* if an I/O error occurs
*/
FileVisitResult visitFileFailed(T file, 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 {@link #visitFile visitFile}
* method returning {@link FileVisitResult#SKIP_SIBLINGS SKIP_SIBLINGS},
* or an I/O error when iterating over the directory).
*
* @param dir
* a reference to the directory
* @param exc
* {@code 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 the visit result
*
* @throws IOException
* if an I/O error occurs
*/
FileVisitResult postVisitDirectory(T dir, IOException exc)
throws IOException;
}