1 /*

     2  * Copyright 2007-2009 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package java.nio.file;

    27 

    28 import java.nio.file.attribute.BasicFileAttributes;

    29 import java.io.IOException;

    30 

    31 /**

    32  * A visitor of files. An implementation of this interface is provided to the

    33  * {@link Files#walkFileTree walkFileTree} utility method to visit each file

    34  * in a tree.

    35  *

    36  * <p> <b>Usage Examples:</b>

    37  * Suppose we want to delete a file tree. In that case, each directory should

    38  * be deleted after the entries in the directory are deleted.

    39  * <pre>

    40  *     Path start = ...

    41  *     Files.walkFileTree(start, new SimpleFileVisitor<Path>() {

    42  *         @Override

    43  *         public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {

    44  *             try {

    45  *                 file.delete(false);

    46  *             } catch (IOException exc) {

    47  *                 // failed to delete

    48  *             }

    49  *             return FileVisitResult.CONTINUE;

    50  *         }

    51  *         @Override

    52  *         public FileVisitResult postVisitDirectory(Path dir, IOException e) {

    53  *             if (e == null) {

    54  *                 try {

    55  *                     dir.delete(false);

    56  *                 } catch (IOException exc) {

    57  *                     // failed to delete

    58  *                 }

    59  *             } else {

    60  *                 // directory iteration failed

    61  *             }

    62  *             return FileVisitResult.CONTINUE;

    63  *         }

    64  *     });

    65  * </pre>

    66  * <p> Furthermore, suppose we want to copy a file tree rooted at a source

    67  * directory to a target location. In that case, symbolic links should be

    68  * followed and the target directory should be created before the entries in

    69  * the directory are copied.

    70  * <pre>

    71  *     final Path source = ...

    72  *     final Path target = ...

    73  *

    74  *     Files.walkFileTree(source, EnumSet.of(FileVisitOption.FOLLOW_LINKS), Integer.MAX_VALUE,

    75  *         new SimpleFileVisitor<Path>() {

    76  *             @Override

    77  *             public FileVisitResult preVisitDirectory(Path dir) {

    78  *                 try {

    79  *                     dir.copyTo(target.resolve(source.relativize(dir)));

    80  *                 } catch (FileAlreadyExistsException e) {

    81  *                      // ignore

    82  *                 } catch (IOException e) {

    83  *                     // copy failed, skip rest of directory and descendants

    84  *                     return SKIP_SUBTREE;

    85  *                 }

    86  *                 return CONTINUE;

    87  *             }

    88  *             @Override

    89  *             public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {

    90  *                 try {

    91  *                     file.copyTo(target.resolve(source.relativize(file)));

    92  *                 } catch (IOException e) {

    93  *                     // copy failed

    94  *                 }

    95  *                 return CONTINUE;

    96  *             }

    97  *         });

    98  * </pre>

    99  *

   100  * @since 1.7

   101  */

   102 

   103 public interface FileVisitor<T extends FileRef> {

   104 

   105     /**

   106      * Invoked for a directory before entries in the directory are visited.

   107      *

   108      * <p> If this method returns {@link FileVisitResult#CONTINUE CONTINUE},

   109      * then entries in the directory are visited. If this method returns {@link

   110      * FileVisitResult#SKIP_SUBTREE SKIP_SUBTREE} or {@link

   111      * FileVisitResult#SKIP_SIBLINGS SKIP_SIBLINGS} then entries in the

   112      * directory (and any descendants) will not be visited.

   113      *

   114      * @param   dir

   115      *          A reference to the directory

   116      *

   117      * @return  the visit result

   118      */

   119     FileVisitResult preVisitDirectory(T dir);

   120 

   121     /**

   122      * Invoked for a directory that could not be opened.

   123      *

   124      * @param   dir

   125      *          A reference to the directory

   126      * @param   exc

   127      *          The I/O exception thrown from the attempt to open the directory

   128      *

   129      * @return  the visit result

   130      */

   131     FileVisitResult preVisitDirectoryFailed(T dir, IOException exc);

   132 

   133     /**

   134      * Invoked for a file in a directory.

   135      *

   136      * @param   file

   137      *          A reference to the file

   138      * @param   attrs

   139      *          The file's basic attributes

   140      *

   141      * @return  the visit result

   142      */

   143     FileVisitResult visitFile(T file, BasicFileAttributes attrs);

   144 

   145     /**

   146      * Invoked for a file when its basic file attributes could not be read.

   147      *

   148      * @param   file

   149      *          A reference to the file

   150      * @param   exc

   151      *          The I/O exception thrown from the attempt to read the file

   152      *          attributes

   153      *

   154      * @return  the visit result

   155      */

   156     FileVisitResult visitFileFailed(T file, IOException exc);

   157 

   158     /**

   159      * Invoked for a directory after entries in the directory, and all of their

   160      * descendants, have been visited. This method is also invoked when iteration

   161      * of the directory completes prematurely (by a {@link #visitFile visitFile}

   162      * method returning {@link FileVisitResult#SKIP_SIBLINGS SKIP_SIBLINGS},

   163      * or an I/O error when iterating over the directory).

   164      *

   165      * @param   dir

   166      *          A reference to the directory

   167      * @param   exc

   168      *          {@code null} if the iteration of the directory completes without

   169      *          an error; otherwise the I/O exception that caused the iteration

   170      *          of the directory to complete prematurely

   171      *

   172      * @return  the visit result

   173      */

   174     FileVisitResult postVisitDirectory(T dir, IOException exc);

   175 }