    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.io;
    018
    019import java.io.File;
    020import java.io.FileFilter;
    021import java.io.IOException;
    022import java.nio.file.Files;
    023import java.util.Collection;
    024import java.util.Objects;
    025
    026import org.apache.commons.io.file.PathUtils;
    027import org.apache.commons.io.filefilter.FileFilterUtils;
    028import org.apache.commons.io.filefilter.IOFileFilter;
    029import org.apache.commons.io.filefilter.TrueFileFilter;
    030
    031/**
    032 * Abstract class that walks through a directory hierarchy and provides subclasses with convenient hooks to add specific
    033 * behavior.
    034 * <p>
    035 * This class operates with a {@link FileFilter} and maximum depth to limit the files and directories visited. Commons
    036 * IO supplies many common filter implementations in the <a href="filefilter/package-summary.html"> filefilter</a>
    037 * package.
    038 * </p>
    039 * <p>
    040 * The following sections describe:
    041 * </p>
    042 * <ul>
    043 * <li><a href="#example">1. Example Implementation</a> - example {@link FileCleaner} implementation.</li>
    044 * <li><a href="#filter">2. Filter Example</a> - using {@link FileFilter}(s) with {@link DirectoryWalker}.</li>
    045 * <li><a href="#cancel">3. Cancellation</a> - how to implement cancellation behavior.</li>
    046 * </ul>
    047 *
    048 * <h2 id="example">1. Example Implementation</h2>
    049 *
    050 * There are many possible extensions, for example, to delete all files and '.svn' directories, and return a list of
    051 * deleted files:
    052 *
    053 * <pre>
    054 * public class FileCleaner extends DirectoryWalker {
    055 *
    056 *     public FileCleaner() {
    057 *         super();
    058 *     }
    059 *
    060 *     public List clean(File startDirectory) {
    061 *         List results = new ArrayList();
    062 *         walk(startDirectory, results);
    063 *         return results;
    064 *     }
    065 *
    066 *     protected boolean handleDirectory(File directory, int depth, Collection results) {
    067 *         // delete svn directories and then skip
    068 *         if (".svn".equals(directory.getName())) {
    069 *             directory.delete();
    070 *             return false;
    071 *         } else {
    072 *             return true;
    073 *         }
    074 *
    075 *     }
    076 *
    077 *     protected void handleFile(File file, int depth, Collection results) {
    078 *         // delete file and add to list of deleted
    079 *         file.delete();
    080 *         results.add(file);
    081 *     }
    082 * }
    083 * </pre>
    084 *
    085 * <h2 id="filter">2. Filter Example</h2>
    086 *
    087 * <p>
    088 * Choosing which directories and files to process can be a key aspect of using this class. This information can be
    089 * setup in three ways, via three different constructors.
    090 * </p>
    091 * <p>
    092 * The first option is to visit all directories and files. This is achieved via the no-args constructor.
    093 * </p>
    094 * <p>
    095 * The second constructor option is to supply a single {@link FileFilter} that describes the files and directories to
    096 * visit. Care must be taken with this option as the same filter is used for both directories and files.
    097 * </p>
    098 * <p>
    099 * For example, if you wanted all directories which are not hidden and files which end in ".txt":
    100 * </p>
    101 *
    102 * <pre>
    103 * public class FooDirectoryWalker extends DirectoryWalker {
    104 *     public FooDirectoryWalker(FileFilter filter) {
    105 *         super(filter, -1);
    106 *     }
    107 * }
    108 *
    109 * // Build up the filters and create the walker
    110 * // Create a filter for Non-hidden directories
    111 * IOFileFilter fooDirFilter = FileFilterUtils.andFileFilter(FileFilterUtils.directoryFileFilter,
    112 *     HiddenFileFilter.VISIBLE);
    113 *
    114 * // Create a filter for Files ending in ".txt"
    115 * IOFileFilter fooFileFilter = FileFilterUtils.andFileFilter(FileFilterUtils.fileFileFilter,
    116 *     FileFilterUtils.suffixFileFilter(".txt"));
    117 *
    118 * // Combine the directory and file filters using an OR condition
    119 * java.io.FileFilter fooFilter = FileFilterUtils.orFileFilter(fooDirFilter, fooFileFilter);
    120 *
    121 * // Use the filter to construct a DirectoryWalker implementation
    122 * FooDirectoryWalker walker = new FooDirectoryWalker(fooFilter);
    123 * </pre>
    124 * <p>
    125 * The third constructor option is to specify separate filters, one for directories and one for files. These are
    126 * combined internally to form the correct {@link FileFilter}, something which is very easy to get wrong when
    127 * attempted manually, particularly when trying to express constructs like 'any file in directories named docs'.
    128 * </p>
    129 * <p>
    130 * For example, if you wanted all directories which are not hidden and files which end in ".txt":
    131 * </p>
    132 *
    133 * <pre>
    134 *  public class FooDirectoryWalker extends DirectoryWalker {
    135 *    public FooDirectoryWalker(IOFileFilter dirFilter, IOFileFilter fileFilter) {
    136 *      super(dirFilter, fileFilter, -1);
    137 *    }
    138 *  }
    139 *
    140 *  // Use the filters to construct the walker
    141 *  FooDirectoryWalker walker = new FooDirectoryWalker(
    142 *    HiddenFileFilter.VISIBLE,
    143 *    FileFilterUtils.suffixFileFilter(".txt"),
    144 *  );
    145 * </pre>
    146 * <p>
    147 * This is much simpler than the previous example, and is why it is the preferred option for filtering.
    148 * </p>
    149 *
    150 * <h2 id="cancel">3. Cancellation</h2>
    151 *
    152 * <p>
    153 * The DirectoryWalker contains some of the logic required for cancel processing. Subclasses must complete the
    154 * implementation.
    155 * </p>
    156 * <p>
    157 * What {@link DirectoryWalker} does provide for cancellation is:
    158 * </p>
    159 * <ul>
    160 * <li>{@link CancelException} which can be thrown in any of the <i>lifecycle</i> methods to stop processing.</li>
    161 * <li>The {@code walk()} method traps thrown {@link CancelException} and calls the {@code handleCancelled()}
    162 * method, providing a place for custom cancel processing.</li>
    163 * </ul>
    164 * <p>
    165 * Implementations need to provide:
    166 * </p>
    167 * <ul>
    168 * <li>The decision logic on whether to cancel processing or not.</li>
    169 * <li>Constructing and throwing a {@link CancelException}.</li>
    170 * <li>Custom cancel processing in the {@code handleCancelled()} method.
    171 * </ul>
    172 * <p>
    173 * Two possible scenarios are envisaged for cancellation:
    174 * </p>
    175 * <ul>
    176 * <li><a href="#external">3.1 External / Multi-threaded</a> - cancellation being decided/initiated by an external
    177 * process.</li>
    178 * <li><a href="#internal">3.2 Internal</a> - cancellation being decided/initiated from within a DirectoryWalker
    179 * implementation.</li>
    180 * </ul>
    181 * <p>
    182 * The following sections provide example implementations for these two different scenarios.
    183 * </p>
    184 *
    185 * <h3 id="external">3.1 External / Multi-threaded</h3>
    186 *
    187 * <p>
    188 * This example provides a public {@code cancel()} method that can be called by another thread to stop the
    189 * processing. A typical example use-case would be a cancel button on a GUI. Calling this method sets a
    190 * <a href="http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#36930"> volatile</a> flag to ensure
    191 * it will work properly in a multi-threaded environment. The flag is returned by the {@code handleIsCancelled()}
    192 * method, which will cause the walk to stop immediately. The {@code handleCancelled()} method will be the next,
    193 * and last, callback method received once cancellation has occurred.
    194 * </p>
    195 *
    196 * <pre>
    197 * public class FooDirectoryWalker extends DirectoryWalker {
    198 *
    199 *     private volatile boolean cancelled = false;
    200 *
    201 *     public void cancel() {
    202 *         cancelled = true;
    203 *     }
    204 *
    205 *     protected boolean handleIsCancelled(File file, int depth, Collection results) {
    206 *         return cancelled;
    207 *     }
    208 *
    209 *     protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
    210 *         // implement processing required when a cancellation occurs
    211 *     }
    212 * }
    213 * </pre>
    214 *
    215 * <h3 id="internal">3.2 Internal</h3>
    216 *
    217 * <p>
    218 * This shows an example of how internal cancellation processing could be implemented. <b>Note</b> the decision logic
    219 * and throwing a {@link CancelException} could be implemented in any of the <i>lifecycle</i> methods.
    220 * </p>
    221 *
    222 * <pre>
    223 * public class BarDirectoryWalker extends DirectoryWalker {
    224 *
    225 *     protected boolean handleDirectory(File directory, int depth, Collection results) throws IOException {
    226 *         // cancel if hidden directory
    227 *         if (directory.isHidden()) {
    228 *             throw new CancelException(file, depth);
    229 *         }
    230 *         return true;
    231 *     }
    232 *
    233 *     protected void handleFile(File file, int depth, Collection results) throws IOException {
    234 *         // cancel if read-only file
    235 *         if (!file.canWrite()) {
    236 *             throw new CancelException(file, depth);
    237 *         }
    238 *         results.add(file);
    239 *     }
    240 *
    241 *     protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
    242 *         // implement processing required when a cancellation occurs
    243 *     }
    244 * }
    245 * </pre>
    246 *
    247 * @param <T> The result type, like {@link File}.
    248 * @since 1.3
    249 * @deprecated Apache Commons IO no longer uses this class. Instead, use
    250 *             {@link PathUtils#walk(java.nio.file.Path, org.apache.commons.io.file.PathFilter, int, boolean, java.nio.file.FileVisitOption...)}
    251 *             or {@link Files#walkFileTree(java.nio.file.Path, java.util.Set, int, java.nio.file.FileVisitor)}, and
    252 *             friends.
    253 */
    254@Deprecated
    255public abstract class DirectoryWalker<T> {
    256
    257    /**
    258     * CancelException is thrown in DirectoryWalker to cancel the current
    259     * processing.
    260     */
    261    public static class CancelException extends IOException {
    262
    263        /** Serialization id. */
    264        private static final long serialVersionUID = 1347339620135041008L;
    265
    266        /** The file being processed when the exception was thrown. */
    267        private final File file;
    268        /** The file depth when the exception was thrown. */
    269        private final int depth;
    270
    271        /**
    272         * Constructs a {@link CancelException} with
    273         * the file and depth when cancellation occurred.
    274         *
    275         * @param file  the file when the operation was cancelled, may be null
    276         * @param depth  the depth when the operation was cancelled, may be null
    277         */
    278        public CancelException(final File file, final int depth) {
    279            this("Operation Cancelled", file, depth);
    280        }
    281
    282        /**
    283         * Constructs a {@link CancelException} with
    284         * an appropriate message and the file and depth when
    285         * cancellation occurred.
    286         *
    287         * @param message  the detail message
    288         * @param file  the file when the operation was cancelled
    289         * @param depth  the depth when the operation was cancelled
    290         */
    291        public CancelException(final String message, final File file, final int depth) {
    292            super(message);
    293            this.file = file;
    294            this.depth = depth;
    295        }
    296
    297        /**
    298         * Returns the depth when the operation was cancelled.
    299         *
    300         * @return the depth when the operation was cancelled
    301         */
    302        public int getDepth() {
    303            return depth;
    304        }
    305
    306        /**
    307         * Returns the file when the operation was cancelled.
    308         *
    309         * @return the file when the operation was cancelled
    310         */
    311        public File getFile() {
    312            return file;
    313        }
    314    }
    315    /**
    316     * The file filter to use to filter files and directories.
    317     */
    318    private final FileFilter filter;
    319
    320    /**
    321     * The limit on the directory depth to walk.
    322     */
    323    private final int depthLimit;
    324
    325    /**
    326     * Constructs an instance with no filtering and unlimited <i>depth</i>.
    327     */
    328    protected DirectoryWalker() {
    329        this(null, -1);
    330    }
    331
    332    /**
    333     * Constructs an instance with a filter and limit the <i>depth</i> navigated to.
    334     * <p>
    335     * The filter controls which files and directories will be navigated to as
    336     * part of the walk. The {@link FileFilterUtils} class is useful for combining
    337     * various filters together. A {@code null} filter means that no
    338     * filtering should occur and all files and directories will be visited.
    339     * </p>
    340     *
    341     * @param filter  the filter to apply, null means visit all files
    342     * @param depthLimit  controls how <i>deep</i> the hierarchy is
    343     *  navigated to (less than 0 means unlimited)
    344     */
    345    protected DirectoryWalker(final FileFilter filter, final int depthLimit) {
    346        this.filter = filter;
    347        this.depthLimit = depthLimit;
    348    }
    349
    350    /**
    351     * Constructs an instance with a directory and a file filter and an optional
    352     * limit on the <i>depth</i> navigated to.
    353     * <p>
    354     * The filters control which files and directories will be navigated to as part
    355     * of the walk. This constructor uses {@link FileFilterUtils#makeDirectoryOnly(IOFileFilter)}
    356     * and {@link FileFilterUtils#makeFileOnly(IOFileFilter)} internally to combine the filters.
    357     * A {@code null} filter means that no filtering should occur.
    358     * </p>
    359     *
    360     * @param directoryFilter  the filter to apply to directories, null means visit all directories
    361     * @param fileFilter  the filter to apply to files, null means visit all files
    362     * @param depthLimit  controls how <i>deep</i> the hierarchy is
    363     *  navigated to (less than 0 means unlimited)
    364     */
    365    protected DirectoryWalker(IOFileFilter directoryFilter, IOFileFilter fileFilter, final int depthLimit) {
    366        if (directoryFilter == null && fileFilter == null) {
    367            this.filter = null;
    368        } else {
    369            directoryFilter = directoryFilter != null ? directoryFilter : TrueFileFilter.TRUE;
    370            fileFilter = fileFilter != null ? fileFilter : TrueFileFilter.TRUE;
    371            directoryFilter = FileFilterUtils.makeDirectoryOnly(directoryFilter);
    372            fileFilter = FileFilterUtils.makeFileOnly(fileFilter);
    373            this.filter = directoryFilter.or(fileFilter);
    374        }
    375        this.depthLimit = depthLimit;
    376    }
    377
    378    /**
    379     * Checks whether the walk has been cancelled by calling {@link #handleIsCancelled},
    380     * throwing a {@link CancelException} if it has.
    381     * <p>
    382     * Writers of subclasses should not normally call this method as it is called
    383     * automatically by the walk of the tree. However, sometimes a single method,
    384     * typically {@link #handleFile}, may take a long time to run. In that case,
    385     * you may wish to check for cancellation by calling this method.
    386     * </p>
    387     *
    388     * @param file  the current file being processed
    389     * @param depth  the current file level (starting directory = 0)
    390     * @param results  the collection of result objects, may be updated
    391     * @throws IOException if an I/O Error occurs
    392     */
    393    protected final void checkIfCancelled(final File file, final int depth, final Collection<T> results) throws
    394            IOException {
    395        if (handleIsCancelled(file, depth, results)) {
    396            throw new CancelException(file, depth);
    397        }
    398    }
    399
    400    /**
    401     * Overridable callback method invoked with the contents of each directory.
    402     * <p>
    403     * This implementation returns the files unchanged
    404     * </p>
    405     *
    406     * @param directory  the current directory being processed
    407     * @param depth  the current directory level (starting directory = 0)
    408     * @param files the files (possibly filtered) in the directory, may be {@code null}
    409     * @return the filtered list of files
    410     * @throws IOException if an I/O Error occurs
    411     * @since 2.0
    412     */
    413    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    414    protected File[] filterDirectoryContents(final File directory, final int depth, final File... files) throws
    415            IOException {
    416        return files;
    417    }
    418
    419    /**
    420     * Overridable callback method invoked when the operation is cancelled.
    421     * The file being processed when the cancellation occurred can be
    422     * obtained from the exception.
    423     * <p>
    424     * This implementation just re-throws the {@link CancelException}.
    425     * </p>
    426     *
    427     * @param startDirectory  the directory that the walk started from
    428     * @param results  the collection of result objects, may be updated
    429     * @param cancel  the exception throw to cancel further processing
    430     * containing details at the point of cancellation.
    431     * @throws IOException if an I/O Error occurs
    432     */
    433    protected void handleCancelled(final File startDirectory, final Collection<T> results,
    434                       final CancelException cancel) throws IOException {
    435        // re-throw exception - overridable by subclass
    436        throw cancel;
    437    }
    438
    439    /**
    440     * Overridable callback method invoked to determine if a directory should be processed.
    441     * <p>
    442     * This method returns a boolean to indicate if the directory should be examined or not.
    443     * If you return false, the entire directory and any subdirectories will be skipped.
    444     * Note that this functionality is in addition to the filtering by file filter.
    445     * </p>
    446     * <p>
    447     * This implementation does nothing and returns true.
    448     * </p>
    449     *
    450     * @param directory  the current directory being processed
    451     * @param depth  the current directory level (starting directory = 0)
    452     * @param results  the collection of result objects, may be updated
    453     * @return true to process this directory, false to skip this directory
    454     * @throws IOException if an I/O Error occurs
    455     */
    456    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    457    protected boolean handleDirectory(final File directory, final int depth, final Collection<T> results) throws
    458            IOException {
    459        // do nothing - overridable by subclass
    460        return true;  // process directory
    461    }
    462
    463    /**
    464     * Overridable callback method invoked at the end of processing each directory.
    465     * <p>
    466     * This implementation does nothing.
    467     * </p>
    468     *
    469     * @param directory  the directory being processed
    470     * @param depth  the current directory level (starting directory = 0)
    471     * @param results  the collection of result objects, may be updated
    472     * @throws IOException if an I/O Error occurs
    473     */
    474    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    475    protected void handleDirectoryEnd(final File directory, final int depth, final Collection<T> results) throws
    476            IOException {
    477        // do nothing - overridable by subclass
    478    }
    479
    480    /**
    481     * Overridable callback method invoked at the start of processing each directory.
    482     * <p>
    483     * This implementation does nothing.
    484     * </p>
    485     *
    486     * @param directory  the current directory being processed
    487     * @param depth  the current directory level (starting directory = 0)
    488     * @param results  the collection of result objects, may be updated
    489     * @throws IOException if an I/O Error occurs
    490     */
    491    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    492    protected void handleDirectoryStart(final File directory, final int depth, final Collection<T> results) throws
    493            IOException {
    494        // do nothing - overridable by subclass
    495    }
    496
    497    /**
    498     * Overridable callback method invoked at the end of processing.
    499     * <p>
    500     * This implementation does nothing.
    501     * </p>
    502     *
    503     * @param results  the collection of result objects, may be updated
    504     * @throws IOException if an I/O Error occurs
    505     */
    506    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    507    protected void handleEnd(final Collection<T> results) throws IOException {
    508        // do nothing - overridable by subclass
    509    }
    510
    511    /**
    512     * Overridable callback method invoked for each (non-directory) file.
    513     * <p>
    514     * This implementation does nothing.
    515     * </p>
    516     *
    517     * @param file  the current file being processed
    518     * @param depth  the current directory level (starting directory = 0)
    519     * @param results  the collection of result objects, may be updated
    520     * @throws IOException if an I/O Error occurs
    521     */
    522    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    523    protected void handleFile(final File file, final int depth, final Collection<T> results) throws IOException {
    524        // do nothing - overridable by subclass
    525    }
    526
    527    /**
    528     * Overridable callback method invoked to determine if the entire walk
    529     * operation should be immediately cancelled.
    530     * <p>
    531     * This method should be implemented by those subclasses that want to
    532     * provide a public {@code cancel()} method available from another
    533     * thread. The design pattern for the subclass should be as follows:
    534     * </p>
    535     * <pre>
    536     *  public class FooDirectoryWalker extends DirectoryWalker {
    537     *    private volatile boolean cancelled = false;
    538     *
    539     *    public void cancel() {
    540     *        cancelled = true;
    541     *    }
    542     *    private void handleIsCancelled(File file, int depth, Collection results) {
    543     *        return cancelled;
    544     *    }
    545     *    protected void handleCancelled(File startDirectory,
    546     *              Collection results, CancelException cancel) {
    547     *        // implement processing required when a cancellation occurs
    548     *    }
    549     *  }
    550     * </pre>
    551     * <p>
    552     * If this method returns true, then the directory walk is immediately
    553     * cancelled. The next callback method will be {@link #handleCancelled}.
    554     * </p>
    555     * <p>
    556     * This implementation returns false.
    557     * </p>
    558     *
    559     * @param file  the file or directory being processed
    560     * @param depth  the current directory level (starting directory = 0)
    561     * @param results  the collection of result objects, may be updated
    562     * @return true if the walk has been cancelled
    563     * @throws IOException if an I/O Error occurs
    564     */
    565    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    566    protected boolean handleIsCancelled(
    567            final File file, final int depth, final Collection<T> results) throws IOException {
    568        // do nothing - overridable by subclass
    569        return false;  // not cancelled
    570    }
    571
    572    /**
    573     * Overridable callback method invoked for each restricted directory.
    574     * <p>
    575     * This implementation does nothing.
    576     * </p>
    577     *
    578     * @param directory  the restricted directory
    579     * @param depth  the current directory level (starting directory = 0)
    580     * @param results  the collection of result objects, may be updated
    581     * @throws IOException if an I/O Error occurs
    582     */
    583    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    584    protected void handleRestricted(final File directory, final int depth, final Collection<T> results) throws
    585            IOException {
    586        // do nothing - overridable by subclass
    587    }
    588
    589    /**
    590     * Overridable callback method invoked at the start of processing.
    591     * <p>
    592     * This implementation does nothing.
    593     * </p>
    594     *
    595     * @param startDirectory  the directory to start from
    596     * @param results  the collection of result objects, may be updated
    597     * @throws IOException if an I/O Error occurs
    598     */
    599    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    600    protected void handleStart(final File startDirectory, final Collection<T> results) throws IOException {
    601        // do nothing - overridable by subclass
    602    }
    603
    604    /**
    605     * Internal method that walks the directory hierarchy in a depth-first manner.
    606     * <p>
    607     * Users of this class do not need to call this method. This method will
    608     * be called automatically by another (public) method on the specific subclass.
    609     * </p>
    610     * <p>
    611     * Writers of subclasses should call this method to start the directory walk.
    612     * Once called, this method will emit events as it walks the hierarchy.
    613     * The event methods have the prefix {@code handle}.
    614     * </p>
    615     *
    616     * @param startDirectory  the directory to start from, not null
    617     * @param results  the collection of result objects, may be updated
    618     * @throws NullPointerException if the start directory is null
    619     * @throws IOException if an I/O Error occurs
    620     */
    621    protected final void walk(final File startDirectory, final Collection<T> results) throws IOException {
    622        Objects.requireNonNull(startDirectory, "startDirectory");
    623        try {
    624            handleStart(startDirectory, results);
    625            walk(startDirectory, 0, results);
    626            handleEnd(results);
    627        } catch(final CancelException cancel) {
    628            handleCancelled(startDirectory, results, cancel);
    629        }
    630    }
    631
    632    /**
    633     * Main recursive method to examine the directory hierarchy.
    634     *
    635     * @param directory  the directory to examine, not null
    636     * @param depth  the directory level (starting directory = 0)
    637     * @param results  the collection of result objects, may be updated
    638     * @throws IOException if an I/O Error occurs
    639     */
    640    private void walk(final File directory, final int depth, final Collection<T> results) throws IOException {
    641        checkIfCancelled(directory, depth, results);
    642        if (handleDirectory(directory, depth, results)) {
    643            handleDirectoryStart(directory, depth, results);
    644            final int childDepth = depth + 1;
    645            if (depthLimit < 0 || childDepth <= depthLimit) {
    646                checkIfCancelled(directory, depth, results);
    647                File[] childFiles = filter == null ? directory.listFiles() : directory.listFiles(filter);
    648                childFiles = filterDirectoryContents(directory, depth, childFiles);
    649                if (childFiles == null) {
    650                    handleRestricted(directory, childDepth, results);
    651                } else {
    652                    for (final File childFile : childFiles) {
    653                        if (childFile.isDirectory()) {
    654                            walk(childFile, childDepth, results);
    655                        } else {
    656                            checkIfCancelled(childFile, childDepth, results);
    657                            handleFile(childFile, childDepth, results);
    658                            checkIfCancelled(childFile, childDepth, results);
    659                        }
    660                    }
    661                }
    662            }
    663            handleDirectoryEnd(directory, depth, results);
    664        }
    665        checkIfCancelled(directory, depth, results);
    666    }
    667}