Java tutorial
/* * 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; }