/* * 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. * *

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 */ public interface FileVisitor { /** * Invoked for a directory before entries in the directory are visited. * *

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; }