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 * 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;

}