    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.util.ArrayDeque;
    021import java.util.ArrayList;
    022import java.util.Arrays;
    023import java.util.Collection;
    024import java.util.Deque;
    025import java.util.List;
    026import java.util.regex.Matcher;
    027import java.util.regex.Pattern;
    028import java.util.stream.Stream;
    029
    030/**
    031 * General file name and file path manipulation utilities. The methods in this class
    032 * operate on strings that represent relative or absolute paths. Nothing in this class
    033 * ever accesses the file system, or depends on whether a path points to a file that exists.
    034 * <p>
    035 * When dealing with file names, you can hit problems when moving from a Windows
    036 * based development machine to a UNIX based production machine.
    037 * This class aims to help avoid those problems.
    038 * </p>
    039 * <p>
    040 * <strong>NOTE</strong>: You may be able to avoid using this class entirely simply by
    041 * using JDK {@link File File} objects and the two argument constructor
    042 * {@link File#File(java.io.File, String) File(File,String)}.
    043 * </p>
    044 * <p>
    045 * Most methods in this class are designed to work the same on both UNIX and Windows.
    046 * Those that don't include 'System', 'Unix', or 'Windows' in their name.
    047 * </p>
    048 * <p>
    049 * Most methods recognize both separators (forward and backslashes), and both
    050 * sets of prefixes. See the Javadoc of each method for details.
    051 * </p>
    052 * <p>
    053 * This class defines six components within a path (sometimes called a file name or a full file name).
    054 * Given an absolute Windows path such as C:\dev\project\file.txt they are:
    055 * </p>
    056 * <ul>
    057 * <li>the full file name, or just file name - C:\dev\project\file.txt</li>
    058 * <li>the prefix - C:\</li>
    059 * <li>the path - dev\project\</li>
    060 * <li>the full path - C:\dev\project\</li>
    061 * <li>the name - file.txt</li>
    062 * <li>the base name - file</li>
    063 * <li>the extension - txt</li>
    064 * </ul>
    065 * <p>
    066 * Given an absolute UNIX path such as /dev/project/file.txt they are:
    067 * </p>
    068 * <ul>
    069 * <li>the full file name, or just file name - /dev/project/file.txt</li>
    070 * <li>the prefix - /</li>
    071 * <li>the path - dev/project</li>
    072 * <li>the full path - /dev/project</li>
    073 * <li>the name - file.txt</li>
    074 * <li>the base name - file</li>
    075 * <li>the extension - txt</li>
    076 * </ul>
    077 * <p>
    078 * Given a relative Windows path such as dev\project\file.txt they are:
    079 * </p>
    080 * <ul>
    081 * <li>the full file name, or just file name - dev\project\file.txt</li>
    082 * <li>the prefix - null</li>
    083 * <li>the path - dev\project\</li>
    084 * <li>the full path - dev\project\</li>
    085 * <li>the name - file.txt</li>
    086 * <li>the base name - file</li>
    087 * <li>the extension - txt</li>
    088 * </ul>
    089 * <p>
    090 * Given an absolute UNIX path such as /dev/project/file.txt they are:
    091 * </p>
    092 * <ul>
    093 * <li>the full path, full file name, or just file name - /dev/project/file.txt</li>
    094 * <li>the prefix - /</li>
    095 * <li>the path - dev/project</li>
    096 * <li>the full path - /dev/project</li>
    097 * <li>the name - file.txt</li>
    098 * <li>the base name - file</li>
    099 * <li>the extension - txt</li>
    100 * </ul>
    101 *
    102 *
    103 * <p>
    104 * This class works best if directory names end with a separator.
    105 * If you omit the last separator, it is impossible to determine if the last component
    106 * corresponds to a file or a directory. This class treats final components
    107 * that do not end with a separator as files, not directories.
    108 * </p>
    109 * <p>
    110 * This class only supports UNIX and Windows style names.
    111 * Prefixes are matched as follows:
    112 * </p>
    113 * <pre>
    114 * Windows:
    115 * a\b\c.txt           --&gt; ""          --&gt; relative
    116 * \a\b\c.txt          --&gt; "\"         --&gt; current drive absolute
    117 * C:a\b\c.txt         --&gt; "C:"        --&gt; drive relative
    118 * C:\a\b\c.txt        --&gt; "C:\"       --&gt; absolute
    119 * \\server\a\b\c.txt  --&gt; "\\server\" --&gt; UNC
    120 *
    121 * Unix:
    122 * a/b/c.txt           --&gt; ""          --&gt; relative
    123 * /a/b/c.txt          --&gt; "/"         --&gt; absolute
    124 * ~/a/b/c.txt         --&gt; "~/"        --&gt; current user
    125 * ~                   --&gt; "~/"        --&gt; current user (slash added)
    126 * ~user/a/b/c.txt     --&gt; "~user/"    --&gt; named user
    127 * ~user               --&gt; "~user/"    --&gt; named user (slash added)
    128 * </pre>
    129 * <p>
    130 * Both prefix styles are matched, irrespective of the machine that you are
    131 * currently running on.
    132 * </p>
    133 *
    134 * @since 1.1
    135 */
    136public class FilenameUtils {
    137
    138    private static final String[] EMPTY_STRING_ARRAY = {};
    139
    140    private static final String EMPTY_STRING = "";
    141
    142    private static final int NOT_FOUND = -1;
    143
    144    /**
    145     * The extension separator character.
    146     * @since 1.4
    147     */
    148    public static final char EXTENSION_SEPARATOR = '.';
    149
    150    /**
    151     * The extension separator String.
    152     * @since 1.4
    153     */
    154    public static final String EXTENSION_SEPARATOR_STR = Character.toString(EXTENSION_SEPARATOR);
    155
    156    /**
    157     * The UNIX separator character.
    158     */
    159    private static final char UNIX_NAME_SEPARATOR = '/';
    160
    161    /**
    162     * The Windows separator character.
    163     */
    164    private static final char WINDOWS_NAME_SEPARATOR = '\\';
    165
    166    /**
    167     * The system separator character.
    168     */
    169    private static final char SYSTEM_NAME_SEPARATOR = File.separatorChar;
    170
    171    /**
    172     * The separator character that is the opposite of the system separator.
    173     */
    174    private static final char OTHER_SEPARATOR = flipSeparator(SYSTEM_NAME_SEPARATOR);
    175
    176    private static final Pattern IPV4_PATTERN = Pattern.compile("^(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})$");
    177
    178    private static final int IPV4_MAX_OCTET_VALUE = 255;
    179
    180    private static final int IPV6_MAX_HEX_GROUPS = 8;
    181
    182    private static final int IPV6_MAX_HEX_DIGITS_PER_GROUP = 4;
    183
    184    private static final int MAX_UNSIGNED_SHORT = 0xffff;
    185
    186    private static final int BASE_16 = 16;
    187
    188    private static final Pattern REG_NAME_PART_PATTERN = Pattern.compile("^[a-zA-Z0-9][a-zA-Z0-9-]*$");
    189
    190    /**
    191     * Concatenates a fileName to a base path using normal command line style rules.
    192     * <p>
    193     * The effect is equivalent to resultant directory after changing
    194     * directory to the first argument, followed by changing directory to
    195     * the second argument.
    196     * </p>
    197     * <p>
    198     * The first argument is the base path, the second is the path to concatenate.
    199     * The returned path is always normalized via {@link #normalize(String)},
    200     * thus {@code ..} is handled.
    201     * </p>
    202     * <p>
    203     * If {@code pathToAdd} is absolute (has an absolute prefix), then
    204     * it will be normalized and returned.
    205     * Otherwise, the paths will be joined, normalized and returned.
    206     * </p>
    207     * <p>
    208     * The output will be the same on both UNIX and Windows except
    209     * for the separator character.
    210     * </p>
    211     * <pre>
    212     * /foo/      + bar        --&gt;  /foo/bar
    213     * /foo       + bar        --&gt;  /foo/bar
    214     * /foo       + /bar       --&gt;  /bar
    215     * /foo       + C:/bar     --&gt;  C:/bar
    216     * /foo       + C:bar      --&gt;  C:bar [1]
    217     * /foo/a/    + ../bar     --&gt;  /foo/bar
    218     * /foo/      + ../../bar  --&gt;  null
    219     * /foo/      + /bar       --&gt;  /bar
    220     * /foo/..    + /bar       --&gt;  /bar
    221     * /foo       + bar/c.txt  --&gt;  /foo/bar/c.txt
    222     * /foo/c.txt + bar        --&gt;  /foo/c.txt/bar [2]
    223     * </pre>
    224     * <p>
    225     * [1] Note that the Windows relative drive prefix is unreliable when
    226     * used with this method.
    227     * </p>
    228     * <p>
    229     * [2] Note that the first parameter must be a path. If it ends with a name, then
    230     * the name will be built into the concatenated path. If this might be a problem,
    231     * use {@link #getFullPath(String)} on the base path argument.
    232     * </p>
    233     *
    234     * @param basePath  the base path to attach to, always treated as a path
    235     * @param fullFileNameToAdd  the file name (or path) to attach to the base
    236     * @return the concatenated path, or null if invalid
    237     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    238     */
    239    public static String concat(final String basePath, final String fullFileNameToAdd) {
    240        final int prefix = getPrefixLength(fullFileNameToAdd);
    241        if (prefix < 0) {
    242            return null;
    243        }
    244        if (prefix > 0) {
    245            return normalize(fullFileNameToAdd);
    246        }
    247        if (basePath == null) {
    248            return null;
    249        }
    250        final int len = basePath.length();
    251        if (len == 0) {
    252            return normalize(fullFileNameToAdd);
    253        }
    254        final char ch = basePath.charAt(len - 1);
    255        if (isSeparator(ch)) {
    256            return normalize(basePath + fullFileNameToAdd);
    257        }
    258        return normalize(basePath + '/' + fullFileNameToAdd);
    259    }
    260
    261    /**
    262     * Determines whether the {@code parent} directory contains the {@code child} (a file or directory).
    263     * This does not read from the file system, and there is no guarantee or expectation that
    264     * these paths actually exist.
    265     * <p>
    266     * The files names are expected to be normalized.
    267     * </p>
    268     *
    269     * Edge cases:
    270     * <ul>
    271     * <li>A {@code directory} must not be null: if null, throw IllegalArgumentException</li>
    272     * <li>A directory does not contain itself: return false</li>
    273     * <li>A null child file is not contained in any parent: return false</li>
    274     * </ul>
    275     *
    276     * @param canonicalParent the path string to consider as the parent.
    277     * @param canonicalChild the path string to consider as the child.
    278     * @return true if the candidate leaf is under the specified composite. False otherwise.
    279     * @since 2.2
    280     * @see FileUtils#directoryContains(File, File)
    281     */
    282    public static boolean directoryContains(final String canonicalParent, final String canonicalChild) {
    283        if (isEmpty(canonicalParent) || isEmpty(canonicalChild)) {
    284            return false;
    285        }
    286
    287        if (IOCase.SYSTEM.checkEquals(canonicalParent, canonicalChild)) {
    288            return false;
    289        }
    290
    291        final char separator = toSeparator(canonicalParent.charAt(0) == UNIX_NAME_SEPARATOR);
    292        final String parentWithEndSeparator = canonicalParent.charAt(canonicalParent.length() - 1) == separator ? canonicalParent : canonicalParent + separator;
    293
    294        return IOCase.SYSTEM.checkStartsWith(canonicalChild, parentWithEndSeparator);
    295    }
    296
    297    /**
    298     * Does the work of getting the path.
    299     *
    300     * @param fileName  the file name
    301     * @param includeSeparator  true to include the end separator
    302     * @return the path
    303     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    304     */
    305    private static String doGetFullPath(final String fileName, final boolean includeSeparator) {
    306        if (fileName == null) {
    307            return null;
    308        }
    309        final int prefix = getPrefixLength(fileName);
    310        if (prefix < 0) {
    311            return null;
    312        }
    313        if (prefix >= fileName.length()) {
    314            if (includeSeparator) {
    315                return getPrefix(fileName);  // add end slash if necessary
    316            }
    317            return fileName;
    318        }
    319        final int index = indexOfLastSeparator(fileName);
    320        if (index < 0) {
    321            return fileName.substring(0, prefix);
    322        }
    323        int end = index + (includeSeparator ?  1 : 0);
    324        if (end == 0) {
    325            end++;
    326        }
    327        return fileName.substring(0, end);
    328    }
    329
    330    /**
    331     * Does the work of getting the path.
    332     *
    333     * @param fileName  the file name
    334     * @param separatorAdd  0 to omit the end separator, 1 to return it
    335     * @return the path
    336     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    337     */
    338    private static String doGetPath(final String fileName, final int separatorAdd) {
    339        if (fileName == null) {
    340            return null;
    341        }
    342        final int prefix = getPrefixLength(fileName);
    343        if (prefix < 0) {
    344            return null;
    345        }
    346        final int index = indexOfLastSeparator(fileName);
    347        final int endIndex = index + separatorAdd;
    348        if (prefix >= fileName.length() || index < 0 || prefix >= endIndex) {
    349            return EMPTY_STRING;
    350        }
    351        return requireNonNullChars(fileName.substring(prefix, endIndex));
    352    }
    353
    354    /**
    355     * Internal method to perform the normalization.
    356     *
    357     * @param fileName  the file name
    358     * @param separator The separator character to use
    359     * @param keepSeparator  true to keep the final separator
    360     * @return the normalized fileName
    361     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    362     */
    363    private static String doNormalize(final String fileName, final char separator, final boolean keepSeparator) {
    364        if (fileName == null) {
    365            return null;
    366        }
    367
    368        requireNonNullChars(fileName);
    369
    370        int size = fileName.length();
    371        if (size == 0) {
    372            return fileName;
    373        }
    374        final int prefix = getPrefixLength(fileName);
    375        if (prefix < 0) {
    376            return null;
    377        }
    378
    379        final char[] array = new char[size + 2];  // +1 for possible extra slash, +2 for arraycopy
    380        fileName.getChars(0, fileName.length(), array, 0);
    381
    382        // fix separators throughout
    383        final char otherSeparator = flipSeparator(separator);
    384        for (int i = 0; i < array.length; i++) {
    385            if (array[i] == otherSeparator) {
    386                array[i] = separator;
    387            }
    388        }
    389
    390        // add extra separator on the end to simplify code below
    391        boolean lastIsDirectory = true;
    392        if (array[size - 1] != separator) {
    393            array[size++] = separator;
    394            lastIsDirectory = false;
    395        }
    396
    397        // adjoining slashes
    398        // If we get here, prefix can only be 0 or greater, size 1 or greater
    399        // If prefix is 0, set loop start to 1 to prevent index errors
    400        for (int i = prefix != 0 ? prefix : 1; i < size; i++) {
    401            if (array[i] == separator && array[i - 1] == separator) {
    402                System.arraycopy(array, i, array, i - 1, size - i);
    403                size--;
    404                i--;
    405            }
    406        }
    407
    408        // dot slash
    409        for (int i = prefix + 1; i < size; i++) {
    410            if (array[i] == separator && array[i - 1] == '.' &&
    411                    (i == prefix + 1 || array[i - 2] == separator)) {
    412                if (i == size - 1) {
    413                    lastIsDirectory = true;
    414                }
    415                System.arraycopy(array, i + 1, array, i - 1, size - i);
    416                size -=2;
    417                i--;
    418            }
    419        }
    420
    421        // double dot slash
    422        outer:
    423        for (int i = prefix + 2; i < size; i++) {
    424            if (array[i] == separator && array[i - 1] == '.' && array[i - 2] == '.' &&
    425                    (i == prefix + 2 || array[i - 3] == separator)) {
    426                if (i == prefix + 2) {
    427                    return null;
    428                }
    429                if (i == size - 1) {
    430                    lastIsDirectory = true;
    431                }
    432                int j;
    433                for (j = i - 4 ; j >= prefix; j--) {
    434                    if (array[j] == separator) {
    435                        // remove b/../ from a/b/../c
    436                        System.arraycopy(array, i + 1, array, j + 1, size - i);
    437                        size -= i - j;
    438                        i = j + 1;
    439                        continue outer;
    440                    }
    441                }
    442                // remove a/../ from a/../c
    443                System.arraycopy(array, i + 1, array, prefix, size - i);
    444                size -= i + 1 - prefix;
    445                i = prefix + 1;
    446            }
    447        }
    448
    449        if (size <= 0) {  // should never be less than 0
    450            return EMPTY_STRING;
    451        }
    452        if (size <= prefix) {  // should never be less than prefix
    453            return new String(array, 0, size);
    454        }
    455        if (lastIsDirectory && keepSeparator) {
    456            return new String(array, 0, size);  // keep trailing separator
    457        }
    458        return new String(array, 0, size - 1);  // lose trailing separator
    459    }
    460
    461    /**
    462     * Checks whether two file names are exactly equal.
    463     * <p>
    464     * No processing is performed on the file names other than comparison.
    465     * This is merely a null-safe case-sensitive string equality.
    466     * </p>
    467     *
    468     * @param fileName1  the first file name, may be null
    469     * @param fileName2  the second file name, may be null
    470     * @return true if the file names are equal, null equals null
    471     * @see IOCase#SENSITIVE
    472     */
    473    public static boolean equals(final String fileName1, final String fileName2) {
    474        return equals(fileName1, fileName2, false, IOCase.SENSITIVE);
    475    }
    476
    477    /**
    478     * Checks whether two file names are equal, optionally normalizing and providing
    479     * control over the case-sensitivity.
    480     *
    481     * @param fileName1  the first file name, may be null
    482     * @param fileName2  the second file name, may be null
    483     * @param normalize  whether to normalize the file names
    484     * @param ioCase  what case sensitivity rule to use, null means case-sensitive
    485     * @return true if the file names are equal, null equals null
    486     * @since 1.3
    487     */
    488    public static boolean equals(String fileName1, String fileName2, final boolean normalize, final IOCase ioCase) {
    489
    490        if (fileName1 == null || fileName2 == null) {
    491            return fileName1 == null && fileName2 == null;
    492        }
    493        if (normalize) {
    494            fileName1 = normalize(fileName1);
    495            if (fileName1 == null) {
    496                return false;
    497            }
    498            fileName2 = normalize(fileName2);
    499            if (fileName2 == null) {
    500                return false;
    501            }
    502        }
    503        return IOCase.value(ioCase, IOCase.SENSITIVE).checkEquals(fileName1, fileName2);
    504    }
    505
    506    /**
    507     * Checks whether two file names are equal after both have been normalized.
    508     * <p>
    509     * Both file names are first passed to {@link #normalize(String)}.
    510     * The check is then performed in a case-sensitive manner.
    511     * </p>
    512     *
    513     * @param fileName1  the first file name, may be null
    514     * @param fileName2  the second file name, may be null
    515     * @return true if the file names are equal, null equals null
    516     * @see IOCase#SENSITIVE
    517     */
    518    public static boolean equalsNormalized(final String fileName1, final String fileName2) {
    519        return equals(fileName1, fileName2, true, IOCase.SENSITIVE);
    520    }
    521
    522    /**
    523     * Checks whether two file names are equal using the case rules of the system
    524     * after both have been normalized.
    525     * <p>
    526     * Both file names are first passed to {@link #normalize(String)}.
    527     * The check is then performed case-sensitively on UNIX and
    528     * case-insensitively on Windows.
    529     * </p>
    530     *
    531     * @param fileName1  the first file name, may be null
    532     * @param fileName2  the second file name, may be null
    533     * @return true if the file names are equal, null equals null
    534     * @see IOCase#SYSTEM
    535     */
    536    public static boolean equalsNormalizedOnSystem(final String fileName1, final String fileName2) {
    537        return equals(fileName1, fileName2, true, IOCase.SYSTEM);
    538    }
    539
    540    /**
    541     * Checks whether two file names are equal using the case rules of the system.
    542     * <p>
    543     * No processing is performed on the file names other than comparison.
    544     * The check is case-sensitive on UNIX and case-insensitive on Windows.
    545     * </p>
    546     *
    547     * @param fileName1  the first file name, may be null
    548     * @param fileName2  the second file name, may be null
    549     * @return true if the file names are equal, null equals null
    550     * @see IOCase#SYSTEM
    551     */
    552    public static boolean equalsOnSystem(final String fileName1, final String fileName2) {
    553        return equals(fileName1, fileName2, false, IOCase.SYSTEM);
    554    }
    555
    556    /**
    557     * Flips the Windows name separator to Linux and vice-versa.
    558     *
    559     * @param ch The Windows or Linux name separator.
    560     * @return The Windows or Linux name separator.
    561     */
    562    static char flipSeparator(final char ch) {
    563        if (ch == UNIX_NAME_SEPARATOR) {
    564            return WINDOWS_NAME_SEPARATOR;
    565        }
    566        if (ch == WINDOWS_NAME_SEPARATOR) {
    567            return UNIX_NAME_SEPARATOR;
    568        }
    569        throw new IllegalArgumentException(String.valueOf(ch));
    570    }
    571
    572    /**
    573     * Special handling for NTFS ADS: Don't accept colon in the file name.
    574     *
    575     * @param fileName a file name
    576     * @return ADS offsets.
    577     */
    578    private static int getAdsCriticalOffset(final String fileName) {
    579        // Step 1: Remove leading path segments.
    580        final int offset1 = fileName.lastIndexOf(SYSTEM_NAME_SEPARATOR);
    581        final int offset2 = fileName.lastIndexOf(OTHER_SEPARATOR);
    582        if (offset1 == -1) {
    583            if (offset2 == -1) {
    584                return 0;
    585            }
    586            return offset2 + 1;
    587        }
    588        if (offset2 == -1) {
    589            return offset1 + 1;
    590        }
    591        return Math.max(offset1, offset2) + 1;
    592    }
    593
    594    /**
    595     * Gets the base name, minus the full path and extension, from a full file name.
    596     * <p>
    597     * This method will handle a path in either UNIX or Windows format.
    598     * The text after the last forward or backslash and before the last dot is returned.
    599     * </p>
    600     * <pre>
    601     * a/b/c.txt --&gt; c
    602     * a\b\c.txt --&gt; c
    603     * a/b/c.foo.txt --&gt; c.foo
    604     * a.txt     --&gt; a
    605     * a/b/c     --&gt; c
    606     * a/b/c/    --&gt; ""
    607     * </pre>
    608     * <p>
    609     * The output will be the same irrespective of the machine that the code is running on.
    610     * </p>
    611     *
    612     * @param fileName  the file name, null returns null
    613     * @return the name of the file without the path, or an empty string if none exists
    614     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    615     */
    616    public static String getBaseName(final String fileName) {
    617        return removeExtension(getName(fileName));
    618    }
    619
    620    /**
    621     * Gets the extension of a fileName.
    622     * <p>
    623     * This method returns the textual part of the file name after the last dot.
    624     * There must be no directory separator after the dot.
    625     * </p>
    626     * <pre>
    627     * foo.txt      --&gt; "txt"
    628     * a/b/c.jpg    --&gt; "jpg"
    629     * a/b.txt/c    --&gt; ""
    630     * a/b/c        --&gt; ""
    631     * </pre>
    632     * <p>
    633     * The output will be the same irrespective of the machine that the code is running on, with the
    634     * exception of a possible {@link IllegalArgumentException} on Windows (see below).
    635     * </p>
    636     * <p>
    637     * <strong>Note:</strong> This method used to have a hidden problem for names like "foo.exe:bar.txt".
    638     * In this case, the name wouldn't be the name of a file, but the identifier of an
    639     * alternate data stream (bar.txt) on the file foo.exe. The method used to return
    640     * ".txt" here, which would be misleading. Commons IO 2.7 and later throw
    641     * an {@link IllegalArgumentException} for names like this.
    642     * </p>
    643     *
    644     * @param fileName the file name to retrieve the extension of.
    645     * @return the extension of the file or an empty string if none exists or {@code null}
    646     * if the file name is {@code null}.
    647     * @throws IllegalArgumentException <strong>Windows only:</strong> the file name parameter is, in fact,
    648     * the identifier of an Alternate Data Stream, for example "foo.exe:bar.txt".
    649     */
    650    public static String getExtension(final String fileName) throws IllegalArgumentException {
    651        if (fileName == null) {
    652            return null;
    653        }
    654        final int index = indexOfExtension(fileName);
    655        if (index == NOT_FOUND) {
    656            return EMPTY_STRING;
    657        }
    658        return fileName.substring(index + 1);
    659    }
    660
    661    /**
    662     * Gets the full path (prefix + path) from a full file name.
    663     * <p>
    664     * This method will handle a file in either UNIX or Windows format.
    665     * The method is entirely text based, and returns the text before and
    666     * including the last forward or backslash.
    667     * </p>
    668     * <pre>
    669     * C:\a\b\c.txt --&gt; C:\a\b\
    670     * ~/a/b/c.txt  --&gt; ~/a/b/
    671     * a.txt        --&gt; ""
    672     * a/b/c        --&gt; a/b/
    673     * a/b/c/       --&gt; a/b/c/
    674     * C:           --&gt; C:
    675     * C:\          --&gt; C:\
    676     * ~            --&gt; ~/
    677     * ~/           --&gt; ~/
    678     * ~user        --&gt; ~user/
    679     * ~user/       --&gt; ~user/
    680     * </pre>
    681     * <p>
    682     * The output will be the same irrespective of the machine that the code is running on.
    683     * </p>
    684     *
    685     * @param fileName  the file name, null returns null
    686     * @return the path of the file, an empty string if none exists, null if invalid
    687     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    688     */
    689    public static String getFullPath(final String fileName) {
    690        return doGetFullPath(fileName, true);
    691    }
    692
    693    /**
    694     * Gets the full path (prefix + path) from a full file name,
    695     * excluding the final directory separator.
    696     * <p>
    697     * This method will handle a file in either UNIX or Windows format.
    698     * The method is entirely text based, and returns the text before the
    699     * last forward or backslash.
    700     * </p>
    701     * <pre>
    702     * C:\a\b\c.txt --&gt; C:\a\b
    703     * ~/a/b/c.txt  --&gt; ~/a/b
    704     * a.txt        --&gt; ""
    705     * a/b/c        --&gt; a/b
    706     * a/b/c/       --&gt; a/b/c
    707     * C:           --&gt; C:
    708     * C:\          --&gt; C:\
    709     * ~            --&gt; ~
    710     * ~/           --&gt; ~
    711     * ~user        --&gt; ~user
    712     * ~user/       --&gt; ~user
    713     * </pre>
    714     * <p>
    715     * The output will be the same irrespective of the machine that the code is running on.
    716     * </p>
    717     *
    718     * @param fileName  the file name, null returns null
    719     * @return the path of the file, an empty string if none exists, null if invalid
    720     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    721     */
    722    public static String getFullPathNoEndSeparator(final String fileName) {
    723        return doGetFullPath(fileName, false);
    724    }
    725
    726    /**
    727     * Gets the name minus the path from a full file name.
    728     * <p>
    729     * This method will handle a file in either UNIX or Windows format.
    730     * The text after the last forward or backslash is returned.
    731     * </p>
    732     * <pre>
    733     * a/b/c.txt --&gt; c.txt
    734     * a\b\c.txt --&gt; c.txt
    735     * a.txt     --&gt; a.txt
    736     * a/b/c     --&gt; c
    737     * a/b/c/    --&gt; ""
    738     * </pre>
    739     * <p>
    740     * The output will be the same irrespective of the machine that the code is running on.
    741     * </p>
    742     *
    743     * @param fileName  the file name, null returns null
    744     * @return the name of the file without the path, or an empty string if none exists
    745     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    746     */
    747    public static String getName(final String fileName) {
    748        if (fileName == null) {
    749            return null;
    750        }
    751        return requireNonNullChars(fileName).substring(indexOfLastSeparator(fileName) + 1);
    752    }
    753
    754    /**
    755     * Gets the path from a full file name, which excludes the prefix and the name.
    756     * <p>
    757     * This method will handle a file in either UNIX or Windows format.
    758     * The method is entirely text based, and returns the text before and
    759     * including the last forward or backslash.
    760     * </p>
    761     * <pre>
    762     * C:\a\b\c.txt --&gt; a\b\
    763     * ~/a/b/c.txt  --&gt; a/b/
    764     * a.txt        --&gt; ""
    765     * a/b/c        --&gt; a/b/
    766     * a/b/c/       --&gt; a/b/c/
    767     * </pre>
    768     * <p>
    769     * The output will be the same irrespective of the machine that the code is running on.
    770     * </p>
    771     * <p>
    772     * This method drops the prefix from the result.
    773     * See {@link #getFullPath(String)} for the method that retains the prefix.
    774     * </p>
    775     *
    776     * @param fileName  the file name, null returns null
    777     * @return the path of the file, an empty string if none exists, null if invalid
    778     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    779     */
    780    public static String getPath(final String fileName) {
    781        return doGetPath(fileName, 1);
    782    }
    783
    784    /**
    785     * Gets the path (which excludes the prefix) from a full file name, and
    786     * also excluding the final directory separator.
    787     * <p>
    788     * This method will handle a file in either UNIX or Windows format.
    789     * The method is entirely text based, and returns the text before the
    790     * last forward or backslash.
    791     * </p>
    792     * <pre>
    793     * C:\a\b\c.txt --&gt; a\b
    794     * ~/a/b/c.txt  --&gt; a/b
    795     * a.txt        --&gt; ""
    796     * a/b/c        --&gt; a/b
    797     * a/b/c/       --&gt; a/b/c
    798     * </pre>
    799     * <p>
    800     * The output will be the same irrespective of the machine that the code is running on.
    801     * </p>
    802     * <p>
    803     * This method drops the prefix from the result.
    804     * See {@link #getFullPathNoEndSeparator(String)} for the method that retains the prefix.
    805     * </p>
    806     *
    807     * @param fileName  the file name, null returns null
    808     * @return the path of the file, an empty string if none exists, null if invalid
    809     * @throws IllegalArgumentException if the result path contains the null character ({@code U+0000})
    810     */
    811    public static String getPathNoEndSeparator(final String fileName) {
    812        return doGetPath(fileName, 0);
    813    }
    814
    815    /**
    816     * Gets the prefix such as {@code C:/} or {@code ~/} from a full file name,
    817     * <p>
    818     * This method will handle a file in either UNIX or Windows format.
    819     * The prefix includes the first slash in the full file name where applicable.
    820     * </p>
    821     * <pre>
    822     * Windows:
    823     * a\b\c.txt           --&gt; ""          --&gt; relative
    824     * \a\b\c.txt          --&gt; "\"         --&gt; current drive absolute
    825     * C:a\b\c.txt         --&gt; "C:"        --&gt; drive relative
    826     * C:\a\b\c.txt        --&gt; "C:\"       --&gt; absolute
    827     * \\server\a\b\c.txt  --&gt; "\\server\" --&gt; UNC
    828     *
    829     * Unix:
    830     * a/b/c.txt           --&gt; ""          --&gt; relative
    831     * /a/b/c.txt          --&gt; "/"         --&gt; absolute
    832     * ~/a/b/c.txt         --&gt; "~/"        --&gt; current user
    833     * ~                   --&gt; "~/"        --&gt; current user (slash added)
    834     * ~user/a/b/c.txt     --&gt; "~user/"    --&gt; named user
    835     * ~user               --&gt; "~user/"    --&gt; named user (slash added)
    836     * </pre>
    837     * <p>
    838     * The output will be the same irrespective of the machine that the code is running on.
    839     * ie. both UNIX and Windows prefixes are matched regardless.
    840     * </p>
    841     *
    842     * @param fileName  the file name, null returns null
    843     * @return the prefix of the file, null if invalid
    844     * @throws IllegalArgumentException if the result contains the null character ({@code U+0000})
    845     */
    846    public static String getPrefix(final String fileName) {
    847        if (fileName == null) {
    848            return null;
    849        }
    850        final int len = getPrefixLength(fileName);
    851        if (len < 0) {
    852            return null;
    853        }
    854        if (len > fileName.length()) {
    855            requireNonNullChars(fileName);
    856            return fileName + UNIX_NAME_SEPARATOR;
    857        }
    858        return requireNonNullChars(fileName.substring(0, len));
    859    }
    860
    861    /**
    862     * Returns the length of the file name prefix, such as {@code C:/} or {@code ~/}.
    863     * <p>
    864     * This method will handle a file in either UNIX or Windows format.
    865     * </p>
    866     * <p>
    867     * The prefix length includes the first slash in the full file name
    868     * if applicable. Thus, it is possible that the length returned is greater
    869     * than the length of the input string.
    870     * </p>
    871     * <pre>
    872     * Windows:
    873     * a\b\c.txt           --&gt; 0           --&gt; relative
    874     * \a\b\c.txt          --&gt; 1           --&gt; current drive absolute
    875     * C:a\b\c.txt         --&gt; 2           --&gt; drive relative
    876     * C:\a\b\c.txt        --&gt; 3           --&gt; absolute
    877     * \\server\a\b\c.txt  --&gt; 9           --&gt; UNC
    878     * \\\a\b\c.txt        --&gt; -1          --&gt; error
    879     *
    880     * Unix:
    881     * a/b/c.txt           --&gt; 0           --&gt; relative
    882     * /a/b/c.txt          --&gt; 1           --&gt; absolute
    883     * ~/a/b/c.txt         --&gt; 2           --&gt; current user
    884     * ~                   --&gt; 2           --&gt; current user (slash added)
    885     * ~user/a/b/c.txt     --&gt; 6           --&gt; named user
    886     * ~user               --&gt; 6           --&gt; named user (slash added)
    887     * //server/a/b/c.txt  --&gt; 9
    888     * ///a/b/c.txt        --&gt; -1          --&gt; error
    889     * C:                  --&gt; 0           --&gt; valid file name as only null character and / are reserved characters
    890     * </pre>
    891     * <p>
    892     * The output will be the same irrespective of the machine that the code is running on.
    893     * ie. both UNIX and Windows prefixes are matched regardless.
    894     * </p>
    895     * <p>
    896     * Note that a leading // (or \\) is used to indicate a UNC name on Windows.
    897     * These must be followed by a server name, so double-slashes are not collapsed
    898     * to a single slash at the start of the file name.
    899     * </p>
    900     *
    901     * @param fileName  the file name to find the prefix in, null returns -1
    902     * @return the length of the prefix, -1 if invalid or null
    903     */
    904    public static int getPrefixLength(final String fileName) {
    905        if (fileName == null) {
    906            return NOT_FOUND;
    907        }
    908        final int len = fileName.length();
    909        if (len == 0) {
    910            return 0;
    911        }
    912        char ch0 = fileName.charAt(0);
    913        if (ch0 == ':') {
    914            return NOT_FOUND;
    915        }
    916        if (len == 1) {
    917            if (ch0 == '~') {
    918                return 2;  // return a length greater than the input
    919            }
    920            return isSeparator(ch0) ? 1 : 0;
    921        }
    922        if (ch0 == '~') {
    923            int posUnix = fileName.indexOf(UNIX_NAME_SEPARATOR, 1);
    924            int posWin = fileName.indexOf(WINDOWS_NAME_SEPARATOR, 1);
    925            if (posUnix == NOT_FOUND && posWin == NOT_FOUND) {
    926                return len + 1;  // return a length greater than the input
    927            }
    928            posUnix = posUnix == NOT_FOUND ? posWin : posUnix;
    929            posWin = posWin == NOT_FOUND ? posUnix : posWin;
    930            return Math.min(posUnix, posWin) + 1;
    931        }
    932        final char ch1 = fileName.charAt(1);
    933        if (ch1 == ':') {
    934            ch0 = Character.toUpperCase(ch0);
    935            if (ch0 >= 'A' && ch0 <= 'Z') {
    936                if (len == 2 && !FileSystem.getCurrent().supportsDriveLetter()) {
    937                    return 0;
    938                }
    939                if (len == 2 || !isSeparator(fileName.charAt(2))) {
    940                    return 2;
    941                }
    942                return 3;
    943            }
    944            if (ch0 == UNIX_NAME_SEPARATOR) {
    945                return 1;
    946            }
    947            return NOT_FOUND;
    948
    949        }
    950        if (!isSeparator(ch0) || !isSeparator(ch1)) {
    951            return isSeparator(ch0) ? 1 : 0;
    952        }
    953        int posUnix = fileName.indexOf(UNIX_NAME_SEPARATOR, 2);
    954        int posWin = fileName.indexOf(WINDOWS_NAME_SEPARATOR, 2);
    955        if (posUnix == NOT_FOUND && posWin == NOT_FOUND || posUnix == 2 || posWin == 2) {
    956            return NOT_FOUND;
    957        }
    958        posUnix = posUnix == NOT_FOUND ? posWin : posUnix;
    959        posWin = posWin == NOT_FOUND ? posUnix : posWin;
    960        final int pos = Math.min(posUnix, posWin) + 1;
    961        final String hostnamePart = fileName.substring(2, pos - 1);
    962        return isValidHostName(hostnamePart) ? pos : NOT_FOUND;
    963    }
    964
    965    /**
    966     * Returns the index of the last extension separator character, which is a dot.
    967     * <p>
    968     * This method also checks that there is no directory separator after the last dot. To do this it uses
    969     * {@link #indexOfLastSeparator(String)} which will handle a file in either UNIX or Windows format.
    970     * </p>
    971     * <p>
    972     * The output will be the same irrespective of the machine that the code is running on, with the
    973     * exception of a possible {@link IllegalArgumentException} on Windows (see below).
    974     * </p>
    975     * <strong>Note:</strong> This method used to have a hidden problem for names like "foo.exe:bar.txt".
    976     * In this case, the name wouldn't be the name of a file, but the identifier of an
    977     * alternate data stream (bar.txt) on the file foo.exe. The method used to return
    978     * ".txt" here, which would be misleading. Commons IO 2.7, and later versions, are throwing
    979     * an {@link IllegalArgumentException} for names like this.
    980     *
    981     * @param fileName
    982     *            the file name to find the last extension separator in, null returns -1
    983     * @return the index of the last extension separator character, or -1 if there is no such character
    984     * @throws IllegalArgumentException <strong>Windows only:</strong> the file name parameter is, in fact,
    985     * the identifier of an Alternate Data Stream, for example "foo.exe:bar.txt".
    986     */
    987    public static int indexOfExtension(final String fileName) throws IllegalArgumentException {
    988        if (fileName == null) {
    989            return NOT_FOUND;
    990        }
    991        if (isSystemWindows()) {
    992            // Special handling for NTFS ADS: Don't accept colon in the file name.
    993            final int offset = fileName.indexOf(':', getAdsCriticalOffset(fileName));
    994            if (offset != -1) {
    995                throw new IllegalArgumentException("NTFS ADS separator (':') in file name is forbidden.");
    996            }
    997        }
    998        final int extensionPos = fileName.lastIndexOf(EXTENSION_SEPARATOR);
    999        final int lastSeparator = indexOfLastSeparator(fileName);
    1000        return lastSeparator > extensionPos ? NOT_FOUND : extensionPos;
    1001    }
    1002
    1003    /**
    1004     * Returns the index of the last directory separator character.
    1005     * <p>
    1006     * This method will handle a file in either UNIX or Windows format.
    1007     * The position of the last forward or backslash is returned.
    1008     * <p>
    1009     * The output will be the same irrespective of the machine that the code is running on.
    1010     *
    1011     * @param fileName  the file name to find the last path separator in, null returns -1
    1012     * @return the index of the last separator character, or -1 if there
    1013     * is no such character
    1014     */
    1015    public static int indexOfLastSeparator(final String fileName) {
    1016        if (fileName == null) {
    1017            return NOT_FOUND;
    1018        }
    1019        final int lastUnixPos = fileName.lastIndexOf(UNIX_NAME_SEPARATOR);
    1020        final int lastWindowsPos = fileName.lastIndexOf(WINDOWS_NAME_SEPARATOR);
    1021        return Math.max(lastUnixPos, lastWindowsPos);
    1022    }
    1023
    1024    private static boolean isEmpty(final String string) {
    1025        return string == null || string.isEmpty();
    1026    }
    1027
    1028    /**
    1029     * Checks whether the extension of the file name is one of those specified.
    1030     * <p>
    1031     * This method obtains the extension as the textual part of the file name
    1032     * after the last dot. There must be no directory separator after the dot.
    1033     * The extension check is case-sensitive on all platforms.
    1034     *
    1035     * @param fileName  the file name, null returns false
    1036     * @param extensions  the extensions to check for, null checks for no extension
    1037     * @return true if the file name is one of the extensions
    1038     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1039     */
    1040    public static boolean isExtension(final String fileName, final Collection<String> extensions) {
    1041        if (fileName == null) {
    1042            return false;
    1043        }
    1044        requireNonNullChars(fileName);
    1045
    1046        if (extensions == null || extensions.isEmpty()) {
    1047            return indexOfExtension(fileName) == NOT_FOUND;
    1048        }
    1049        return extensions.contains(getExtension(fileName));
    1050    }
    1051
    1052    /**
    1053     * Checks whether the extension of the file name is that specified.
    1054     * <p>
    1055     * This method obtains the extension as the textual part of the file name
    1056     * after the last dot. There must be no directory separator after the dot.
    1057     * The extension check is case-sensitive on all platforms.
    1058     *
    1059     * @param fileName  the file name, null returns false
    1060     * @param extension  the extension to check for, null or empty checks for no extension
    1061     * @return true if the file name has the specified extension
    1062     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1063     */
    1064    public static boolean isExtension(final String fileName, final String extension) {
    1065        if (fileName == null) {
    1066            return false;
    1067        }
    1068        requireNonNullChars(fileName);
    1069
    1070        if (isEmpty(extension)) {
    1071            return indexOfExtension(fileName) == NOT_FOUND;
    1072        }
    1073        return getExtension(fileName).equals(extension);
    1074    }
    1075
    1076    /**
    1077     * Checks whether the extension of the file name is one of those specified.
    1078     * <p>
    1079     * This method obtains the extension as the textual part of the file name
    1080     * after the last dot. There must be no directory separator after the dot.
    1081     * The extension check is case-sensitive on all platforms.
    1082     *
    1083     * @param fileName  the file name, null returns false
    1084     * @param extensions  the extensions to check for, null checks for no extension
    1085     * @return true if the file name is one of the extensions
    1086     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1087     */
    1088    public static boolean isExtension(final String fileName, final String... extensions) {
    1089        if (fileName == null) {
    1090            return false;
    1091        }
    1092        requireNonNullChars(fileName);
    1093
    1094        if (extensions == null || extensions.length == 0) {
    1095            return indexOfExtension(fileName) == NOT_FOUND;
    1096        }
    1097        final String fileExt = getExtension(fileName);
    1098        return Stream.of(extensions).anyMatch(fileExt::equals);
    1099    }
    1100
    1101    /**
    1102     * Checks whether a given string represents a valid IPv4 address.
    1103     *
    1104     * @param name the name to validate
    1105     * @return true if the given name is a valid IPv4 address
    1106     */
    1107    // mostly copied from org.apache.commons.validator.routines.InetAddressValidator#isValidInet4Address
    1108    private static boolean isIPv4Address(final String name) {
    1109        final Matcher m = IPV4_PATTERN.matcher(name);
    1110        if (!m.matches() || m.groupCount() != 4) {
    1111            return false;
    1112        }
    1113
    1114        // verify that address subgroups are legal
    1115        for (int i = 1; i <= 4; i++) {
    1116            final String ipSegment = m.group(i);
    1117            final int iIpSegment = Integer.parseInt(ipSegment);
    1118            if (iIpSegment > IPV4_MAX_OCTET_VALUE) {
    1119                return false;
    1120            }
    1121
    1122            if (ipSegment.length() > 1 && ipSegment.startsWith("0")) {
    1123                return false;
    1124            }
    1125
    1126        }
    1127
    1128        return true;
    1129    }
    1130
    1131    // copied from org.apache.commons.validator.routines.InetAddressValidator#isValidInet6Address
    1132    /**
    1133     * Checks whether a given string represents a valid IPv6 address.
    1134     *
    1135     * @param inet6Address the name to validate
    1136     * @return true if the given name is a valid IPv6 address
    1137     */
    1138    private static boolean isIPv6Address(final String inet6Address) {
    1139        final boolean containsCompressedZeroes = inet6Address.contains("::");
    1140        if (containsCompressedZeroes && inet6Address.indexOf("::") != inet6Address.lastIndexOf("::")) {
    1141            return false;
    1142        }
    1143        if (inet6Address.startsWith(":") && !inet6Address.startsWith("::")
    1144                || inet6Address.endsWith(":") && !inet6Address.endsWith("::")) {
    1145            return false;
    1146        }
    1147        String[] octets = inet6Address.split(":");
    1148        if (containsCompressedZeroes) {
    1149            final List<String> octetList = new ArrayList<>(Arrays.asList(octets));
    1150            if (inet6Address.endsWith("::")) {
    1151                // String.split() drops ending empty segments
    1152                octetList.add("");
    1153            } else if (inet6Address.startsWith("::") && !octetList.isEmpty()) {
    1154                octetList.remove(0);
    1155            }
    1156            octets = octetList.toArray(EMPTY_STRING_ARRAY);
    1157        }
    1158        if (octets.length > IPV6_MAX_HEX_GROUPS) {
    1159            return false;
    1160        }
    1161        int validOctets = 0;
    1162        int emptyOctets = 0; // consecutive empty chunks
    1163        for (int index = 0; index < octets.length; index++) {
    1164            final String octet = octets[index];
    1165            if (octet.isEmpty()) {
    1166                emptyOctets++;
    1167                if (emptyOctets > 1) {
    1168                    return false;
    1169                }
    1170            } else {
    1171                emptyOctets = 0;
    1172                // Is last chunk an IPv4 address?
    1173                if (index == octets.length - 1 && octet.contains(".")) {
    1174                    if (!isIPv4Address(octet)) {
    1175                        return false;
    1176                    }
    1177                    validOctets += 2;
    1178                    continue;
    1179                }
    1180                if (octet.length() > IPV6_MAX_HEX_DIGITS_PER_GROUP) {
    1181                    return false;
    1182                }
    1183                final int octetInt;
    1184                try {
    1185                    octetInt = Integer.parseInt(octet, BASE_16);
    1186                } catch (final NumberFormatException e) {
    1187                    return false;
    1188                }
    1189                if (octetInt < 0 || octetInt > MAX_UNSIGNED_SHORT) {
    1190                    return false;
    1191                }
    1192            }
    1193            validOctets++;
    1194        }
    1195        return validOctets <= IPV6_MAX_HEX_GROUPS && (validOctets >= IPV6_MAX_HEX_GROUPS || containsCompressedZeroes);
    1196    }
    1197
    1198    /**
    1199     * Checks whether a given string is a valid host name according to
    1200     * RFC 3986 - not accepting IP addresses.
    1201     *
    1202     * @see "https://tools.ietf.org/html/rfc3986#section-3.2.2"
    1203     * @param name the hostname to validate
    1204     * @return true if the given name is a valid host name
    1205     */
    1206    private static boolean isRFC3986HostName(final String name) {
    1207        final String[] parts = name.split("\\.", -1);
    1208        for (int i = 0; i < parts.length; i++) {
    1209            if (parts[i].isEmpty()) {
    1210                // trailing dot is legal, otherwise we've hit a .. sequence
    1211                return i == parts.length - 1;
    1212            }
    1213            if (!REG_NAME_PART_PATTERN.matcher(parts[i]).matches()) {
    1214                return false;
    1215            }
    1216        }
    1217        return true;
    1218    }
    1219
    1220    /**
    1221     * Checks if the character is a separator.
    1222     *
    1223     * @param ch  the character to check
    1224     * @return true if it is a separator character
    1225     */
    1226    private static boolean isSeparator(final char ch) {
    1227        return ch == UNIX_NAME_SEPARATOR || ch == WINDOWS_NAME_SEPARATOR;
    1228    }
    1229
    1230    /**
    1231     * Determines if Windows file system is in use.
    1232     *
    1233     * @return true if the system is Windows
    1234     */
    1235    static boolean isSystemWindows() {
    1236        return SYSTEM_NAME_SEPARATOR == WINDOWS_NAME_SEPARATOR;
    1237    }
    1238
    1239    /**
    1240     * Checks whether a given string is a valid host name according to
    1241     * RFC 3986.
    1242     *
    1243     * <p>Accepted are IP addresses (v4 and v6) as well as what the
    1244     * RFC calls a "reg-name". Percent encoded names don't seem to be
    1245     * valid names in UNC paths.</p>
    1246     *
    1247     * @see "https://tools.ietf.org/html/rfc3986#section-3.2.2"
    1248     * @param name the hostname to validate
    1249     * @return true if the given name is a valid host name
    1250     */
    1251    private static boolean isValidHostName(final String name) {
    1252        return isIPv6Address(name) || isRFC3986HostName(name);
    1253    }
    1254
    1255    /**
    1256     * Normalizes a path, removing double and single dot path steps.
    1257     * <p>
    1258     * This method normalizes a path to a standard format.
    1259     * The input may contain separators in either UNIX or Windows format.
    1260     * The output will contain separators in the format of the system.
    1261     * <p>
    1262     * A trailing slash will be retained.
    1263     * A double slash will be merged to a single slash (but UNC names are handled).
    1264     * A single dot path segment will be removed.
    1265     * A double dot will cause that path segment and the one before to be removed.
    1266     * If the double dot has no parent path segment, {@code null} is returned.
    1267     * <p>
    1268     * The output will be the same on both UNIX and Windows except
    1269     * for the separator character.
    1270     * <pre>
    1271     * /foo//               --&gt;   /foo/
    1272     * /foo/./              --&gt;   /foo/
    1273     * /foo/../bar          --&gt;   /bar
    1274     * /foo/../bar/         --&gt;   /bar/
    1275     * /foo/../bar/../baz   --&gt;   /baz
    1276     * //foo//./bar         --&gt;   //foo/bar
    1277     * /../                 --&gt;   null
    1278     * ../foo               --&gt;   null
    1279     * foo/bar/..           --&gt;   foo/
    1280     * foo/../../bar        --&gt;   null
    1281     * foo/../bar           --&gt;   bar
    1282     * //server/foo/../bar  --&gt;   //server/bar
    1283     * //server/../bar      --&gt;   null
    1284     * C:\foo\..\bar        --&gt;   C:\bar
    1285     * C:\..\bar            --&gt;   null
    1286     * ~/foo/../bar/        --&gt;   ~/bar/
    1287     * ~/../bar             --&gt;   null
    1288     * </pre>
    1289     * (Note the file separator will be correct for Windows/Unix.)
    1290     *
    1291     * @param fileName  the file name to normalize, null returns null
    1292     * @return the normalized fileName, or null if invalid
    1293     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1294     */
    1295    public static String normalize(final String fileName) {
    1296        return doNormalize(fileName, SYSTEM_NAME_SEPARATOR, true);
    1297    }
    1298
    1299    /**
    1300     * Normalizes a path, removing double and single dot path steps.
    1301     * <p>
    1302     * This method normalizes a path to a standard format.
    1303     * The input may contain separators in either UNIX or Windows format.
    1304     * The output will contain separators in the format specified.
    1305     * <p>
    1306     * A trailing slash will be retained.
    1307     * A double slash will be merged to a single slash (but UNC names are handled).
    1308     * A single dot path segment will be removed.
    1309     * A double dot will cause that path segment and the one before to be removed.
    1310     * If the double dot has no parent path segment to work with, {@code null}
    1311     * is returned.
    1312     * <p>
    1313     * The output will be the same on both UNIX and Windows except
    1314     * for the separator character.
    1315     * <pre>
    1316     * /foo//               --&gt;   /foo/
    1317     * /foo/./              --&gt;   /foo/
    1318     * /foo/../bar          --&gt;   /bar
    1319     * /foo/../bar/         --&gt;   /bar/
    1320     * /foo/../bar/../baz   --&gt;   /baz
    1321     * //foo//./bar         --&gt;   /foo/bar
    1322     * /../                 --&gt;   null
    1323     * ../foo               --&gt;   null
    1324     * foo/bar/..           --&gt;   foo/
    1325     * foo/../../bar        --&gt;   null
    1326     * foo/../bar           --&gt;   bar
    1327     * //server/foo/../bar  --&gt;   //server/bar
    1328     * //server/../bar      --&gt;   null
    1329     * C:\foo\..\bar        --&gt;   C:\bar
    1330     * C:\..\bar            --&gt;   null
    1331     * ~/foo/../bar/        --&gt;   ~/bar/
    1332     * ~/../bar             --&gt;   null
    1333     * </pre>
    1334     * The output will be the same on both UNIX and Windows including
    1335     * the separator character.
    1336     *
    1337     * @param fileName  the file name to normalize, null returns null
    1338     * @param unixSeparator {@code true} if a UNIX separator should
    1339     * be used or {@code false} if a Windows separator should be used.
    1340     * @return the normalized fileName, or null if invalid
    1341     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1342     * @since 2.0
    1343     */
    1344    public static String normalize(final String fileName, final boolean unixSeparator) {
    1345        return doNormalize(fileName, toSeparator(unixSeparator), true);
    1346    }
    1347
    1348    /**
    1349     * Normalizes a path, removing double and single dot path steps,
    1350     * and removing any final directory separator.
    1351     * <p>
    1352     * This method normalizes a path to a standard format.
    1353     * The input may contain separators in either UNIX or Windows format.
    1354     * The output will contain separators in the format of the system.
    1355     * <p>
    1356     * A trailing slash will be removed.
    1357     * A double slash will be merged to a single slash (but UNC names are handled).
    1358     * A single dot path segment will be removed.
    1359     * A double dot will cause that path segment and the one before to be removed.
    1360     * If the double dot has no parent path segment to work with, {@code null}
    1361     * is returned.
    1362     * <p>
    1363     * The output will be the same on both UNIX and Windows except
    1364     * for the separator character.
    1365     * <pre>
    1366     * /foo//               --&gt;   /foo
    1367     * /foo/./              --&gt;   /foo
    1368     * /foo/../bar          --&gt;   /bar
    1369     * /foo/../bar/         --&gt;   /bar
    1370     * /foo/../bar/../baz   --&gt;   /baz
    1371     * //foo//./bar         --&gt;   /foo/bar
    1372     * /../                 --&gt;   null
    1373     * ../foo               --&gt;   null
    1374     * foo/bar/..           --&gt;   foo
    1375     * foo/../../bar        --&gt;   null
    1376     * foo/../bar           --&gt;   bar
    1377     * //server/foo/../bar  --&gt;   //server/bar
    1378     * //server/../bar      --&gt;   null
    1379     * C:\foo\..\bar        --&gt;   C:\bar
    1380     * C:\..\bar            --&gt;   null
    1381     * ~/foo/../bar/        --&gt;   ~/bar
    1382     * ~/../bar             --&gt;   null
    1383     * </pre>
    1384     * (Note the file separator returned will be correct for Windows/Unix)
    1385     *
    1386     * @param fileName  the file name to normalize, null returns null
    1387     * @return the normalized fileName, or null if invalid
    1388     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1389     */
    1390    public static String normalizeNoEndSeparator(final String fileName) {
    1391        return doNormalize(fileName, SYSTEM_NAME_SEPARATOR, false);
    1392    }
    1393
    1394    /**
    1395     * Normalizes a path, removing double and single dot path steps,
    1396     * and removing any final directory separator.
    1397     * <p>
    1398     * This method normalizes a path to a standard format.
    1399     * The input may contain separators in either UNIX or Windows format.
    1400     * The output will contain separators in the format specified.
    1401     * <p>
    1402     * A trailing slash will be removed.
    1403     * A double slash will be merged to a single slash (but UNC names are handled).
    1404     * A single dot path segment will be removed.
    1405     * A double dot will cause that path segment and the one before to be removed.
    1406     * If the double dot has no parent path segment to work with, {@code null}
    1407     * is returned.
    1408     * <p>
    1409     * The output will be the same on both UNIX and Windows including
    1410     * the separator character.
    1411     * <pre>
    1412     * /foo//               --&gt;   /foo
    1413     * /foo/./              --&gt;   /foo
    1414     * /foo/../bar          --&gt;   /bar
    1415     * /foo/../bar/         --&gt;   /bar
    1416     * /foo/../bar/../baz   --&gt;   /baz
    1417     * //foo//./bar         --&gt;   /foo/bar
    1418     * /../                 --&gt;   null
    1419     * ../foo               --&gt;   null
    1420     * foo/bar/..           --&gt;   foo
    1421     * foo/../../bar        --&gt;   null
    1422     * foo/../bar           --&gt;   bar
    1423     * //server/foo/../bar  --&gt;   //server/bar
    1424     * //server/../bar      --&gt;   null
    1425     * C:\foo\..\bar        --&gt;   C:\bar
    1426     * C:\..\bar            --&gt;   null
    1427     * ~/foo/../bar/        --&gt;   ~/bar
    1428     * ~/../bar             --&gt;   null
    1429     * </pre>
    1430     *
    1431     * @param fileName  the file name to normalize, null returns null
    1432     * @param unixSeparator {@code true} if a UNIX separator should
    1433     * be used or {@code false} if a Windows separator should be used.
    1434     * @return the normalized fileName, or null if invalid
    1435     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1436     * @since 2.0
    1437     */
    1438    public static String normalizeNoEndSeparator(final String fileName, final boolean unixSeparator) {
    1439         return doNormalize(fileName, toSeparator(unixSeparator), false);
    1440    }
    1441
    1442    /**
    1443     * Removes the extension from a fileName.
    1444     * <p>
    1445     * This method returns the textual part of the file name before the last dot.
    1446     * There must be no directory separator after the dot.
    1447     * <pre>
    1448     * foo.txt    --&gt; foo
    1449     * .txt       --&gt; "" (empty string)
    1450     * a\b\c.jpg  --&gt; a\b\c
    1451     * /a/b/c.jpg --&gt; /a/b/c
    1452     * a\b\c      --&gt; a\b\c
    1453     * a.b\c      --&gt; a.b\c
    1454     * </pre>
    1455     * <p>
    1456     * The output will be the same irrespective of the machine that the code is running on.
    1457     *
    1458     * @param fileName  the file name, null returns null
    1459     * @return the file name minus the extension
    1460     * @throws IllegalArgumentException if the file name contains the null character ({@code U+0000})
    1461     */
    1462    public static String removeExtension(final String fileName) {
    1463        if (fileName == null) {
    1464            return null;
    1465        }
    1466        requireNonNullChars(fileName);
    1467
    1468        final int index = indexOfExtension(fileName);
    1469        if (index == NOT_FOUND) {
    1470            return fileName;
    1471        }
    1472        return fileName.substring(0, index);
    1473    }
    1474
    1475    /**
    1476     * Checks the input for null characters ({@code U+0000}), a sign of unsanitized data being passed to file level functions.
    1477     *
    1478     * This may be used to defend against poison byte attacks.
    1479     *
    1480     * @param path the path to check
    1481     * @return The input
    1482     * @throws IllegalArgumentException if path contains the null character ({@code U+0000})
    1483     */
    1484    private static String requireNonNullChars(final String path) {
    1485        if (path.indexOf(0) >= 0) {
    1486            throw new IllegalArgumentException(
    1487                "Null character present in file/path name. There are no known legitimate use cases for such data, but several injection attacks may use it");
    1488        }
    1489        return path;
    1490    }
    1491
    1492    /**
    1493     * Converts all separators to the system separator.
    1494     *
    1495     * @param path the path to be changed, null ignored.
    1496     * @return the updated path.
    1497     */
    1498    public static String separatorsToSystem(final String path) {
    1499        return FileSystem.getCurrent().normalizeSeparators(path);
    1500    }
    1501
    1502    /**
    1503     * Converts all separators to the UNIX separator of forward slash.
    1504     *
    1505     * @param path the path to be changed, null ignored.
    1506     * @return the new path.
    1507     */
    1508    public static String separatorsToUnix(final String path) {
    1509        return FileSystem.LINUX.normalizeSeparators(path);
    1510    }
    1511
    1512    /**
    1513     * Converts all separators to the Windows separator of backslash.
    1514     *
    1515     * @param path the path to be changed, null ignored.
    1516     * @return the updated path.
    1517     */
    1518    public static String separatorsToWindows(final String path) {
    1519        return FileSystem.WINDOWS.normalizeSeparators(path);
    1520    }
    1521
    1522    /**
    1523     * Splits a string into a number of tokens.
    1524     * The text is split by '?' and '*'.
    1525     * Where multiple '*' occur consecutively they are collapsed into a single '*'.
    1526     *
    1527     * @param text  the text to split
    1528     * @return the array of tokens, never null
    1529     */
    1530    static String[] splitOnTokens(final String text) {
    1531        // used by wildcardMatch
    1532        // package level so a unit test may run on this
    1533
    1534        if (text.indexOf('?') == NOT_FOUND && text.indexOf('*') == NOT_FOUND) {
    1535            return new String[] { text };
    1536        }
    1537
    1538        final char[] array = text.toCharArray();
    1539        final ArrayList<String> list = new ArrayList<>();
    1540        final StringBuilder buffer = new StringBuilder();
    1541        char prevChar = 0;
    1542        for (final char ch : array) {
    1543            if (ch == '?' || ch == '*') {
    1544                if (buffer.length() != 0) {
    1545                    list.add(buffer.toString());
    1546                    buffer.setLength(0);
    1547                }
    1548                if (ch == '?') {
    1549                    list.add("?");
    1550                } else if (prevChar != '*') {// ch == '*' here; check if previous char was '*'
    1551                    list.add("*");
    1552                }
    1553            } else {
    1554                buffer.append(ch);
    1555            }
    1556            prevChar = ch;
    1557        }
    1558        if (buffer.length() != 0) {
    1559            list.add(buffer.toString());
    1560        }
    1561
    1562        return list.toArray(EMPTY_STRING_ARRAY);
    1563    }
    1564
    1565    /**
    1566     * Returns '/' if given true, '\\' otherwise.
    1567     *
    1568     * @param unixSeparator which separator to return.
    1569     * @return '/' if given true, '\\' otherwise.
    1570     */
    1571    private static char toSeparator(final boolean unixSeparator) {
    1572        return unixSeparator ? UNIX_NAME_SEPARATOR : WINDOWS_NAME_SEPARATOR;
    1573    }
    1574
    1575    /**
    1576     * Checks a fileName to see if it matches the specified wildcard matcher,
    1577     * always testing case-sensitive.
    1578     * <p>
    1579     * The wildcard matcher uses the characters '?' and '*' to represent a
    1580     * single or multiple (zero or more) wildcard characters.
    1581     * This is the same as often found on DOS/Unix command lines.
    1582     * The check is case-sensitive always.
    1583     * <pre>
    1584     * wildcardMatch("c.txt", "*.txt")      --&gt; true
    1585     * wildcardMatch("c.txt", "*.jpg")      --&gt; false
    1586     * wildcardMatch("a/b/c.txt", "a/b/*")  --&gt; true
    1587     * wildcardMatch("c.txt", "*.???")      --&gt; true
    1588     * wildcardMatch("c.txt", "*.????")     --&gt; false
    1589     * </pre>
    1590     * N.B. the sequence "*?" does not work properly at present in match strings.
    1591     *
    1592     * @param fileName  the file name to match on
    1593     * @param wildcardMatcher  the wildcard string to match against
    1594     * @return true if the file name matches the wildcard string
    1595     * @see IOCase#SENSITIVE
    1596     */
    1597    public static boolean wildcardMatch(final String fileName, final String wildcardMatcher) {
    1598        return wildcardMatch(fileName, wildcardMatcher, IOCase.SENSITIVE);
    1599    }
    1600
    1601    /**
    1602     * Checks a fileName to see if it matches the specified wildcard matcher
    1603     * allowing control over case-sensitivity.
    1604     * <p>
    1605     * The wildcard matcher uses the characters '?' and '*' to represent a
    1606     * single or multiple (zero or more) wildcard characters.
    1607     * N.B. the sequence "*?" does not work properly at present in match strings.
    1608     *
    1609     * @param fileName  the file name to match on
    1610     * @param wildcardMatcher  the wildcard string to match against
    1611     * @param ioCase  what case sensitivity rule to use, null means case-sensitive
    1612     * @return true if the file name matches the wildcard string
    1613     * @since 1.3
    1614     */
    1615    public static boolean wildcardMatch(final String fileName, final String wildcardMatcher, IOCase ioCase) {
    1616        if (fileName == null && wildcardMatcher == null) {
    1617            return true;
    1618        }
    1619        if (fileName == null || wildcardMatcher == null) {
    1620            return false;
    1621        }
    1622        ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
    1623        final String[] wcs = splitOnTokens(wildcardMatcher);
    1624        boolean anyChars = false;
    1625        int textIdx = 0;
    1626        int wcsIdx = 0;
    1627        final Deque<int[]> backtrack = new ArrayDeque<>(wcs.length);
    1628
    1629        // loop around a backtrack stack, to handle complex * matching
    1630        do {
    1631            if (!backtrack.isEmpty()) {
    1632                final int[] array = backtrack.pop();
    1633                wcsIdx = array[0];
    1634                textIdx = array[1];
    1635                anyChars = true;
    1636            }
    1637
    1638            // loop whilst tokens and text left to process
    1639            while (wcsIdx < wcs.length) {
    1640
    1641                if (wcs[wcsIdx].equals("?")) {
    1642                    // ? so move to next text char
    1643                    textIdx++;
    1644                    if (textIdx > fileName.length()) {
    1645                        break;
    1646                    }
    1647                    anyChars = false;
    1648
    1649                } else if (wcs[wcsIdx].equals("*")) {
    1650                    // set any chars status
    1651                    anyChars = true;
    1652                    if (wcsIdx == wcs.length - 1) {
    1653                        textIdx = fileName.length();
    1654                    }
    1655
    1656                } else {
    1657                    // matching text token
    1658                    if (anyChars) {
    1659                        // any chars then try to locate text token
    1660                        textIdx = ioCase.checkIndexOf(fileName, textIdx, wcs[wcsIdx]);
    1661                        if (textIdx == NOT_FOUND) {
    1662                            // token not found
    1663                            break;
    1664                        }
    1665                        final int repeat = ioCase.checkIndexOf(fileName, textIdx + 1, wcs[wcsIdx]);
    1666                        if (repeat >= 0) {
    1667                            backtrack.push(new int[] {wcsIdx, repeat});
    1668                        }
    1669                    } else if (!ioCase.checkRegionMatches(fileName, textIdx, wcs[wcsIdx])) {
    1670                        // matching from current position
    1671                        // couldn't match token
    1672                        break;
    1673                    }
    1674
    1675                    // matched text token, move text index to end of matched token
    1676                    textIdx += wcs[wcsIdx].length();
    1677                    anyChars = false;
    1678                }
    1679
    1680                wcsIdx++;
    1681            }
    1682
    1683            // full match
    1684            if (wcsIdx == wcs.length && textIdx == fileName.length()) {
    1685                return true;
    1686            }
    1687
    1688        } while (!backtrack.isEmpty());
    1689
    1690        return false;
    1691    }
    1692
    1693    /**
    1694     * Checks a fileName to see if it matches the specified wildcard matcher
    1695     * using the case rules of the system.
    1696     * <p>
    1697     * The wildcard matcher uses the characters '?' and '*' to represent a
    1698     * single or multiple (zero or more) wildcard characters.
    1699     * This is the same as often found on DOS/Unix command lines.
    1700     * The check is case-sensitive on UNIX and case-insensitive on Windows.
    1701     * <pre>
    1702     * wildcardMatch("c.txt", "*.txt")      --&gt; true
    1703     * wildcardMatch("c.txt", "*.jpg")      --&gt; false
    1704     * wildcardMatch("a/b/c.txt", "a/b/*")  --&gt; true
    1705     * wildcardMatch("c.txt", "*.???")      --&gt; true
    1706     * wildcardMatch("c.txt", "*.????")     --&gt; false
    1707     * </pre>
    1708     * N.B. the sequence "*?" does not work properly at present in match strings.
    1709     *
    1710     * @param fileName  the file name to match on
    1711     * @param wildcardMatcher  the wildcard string to match against
    1712     * @return true if the file name matches the wildcard string
    1713     * @see IOCase#SYSTEM
    1714     */
    1715    public static boolean wildcardMatchOnSystem(final String fileName, final String wildcardMatcher) {
    1716        return wildcardMatch(fileName, wildcardMatcher, IOCase.SYSTEM);
    1717    }
    1718
    1719    /**
    1720     * Instances should NOT be constructed in standard programming.
    1721     *
    1722     * @deprecated TODO Make private in 3.0.
    1723     */
    1724    @Deprecated
    1725    public FilenameUtils() {
    1726        // empty
    1727    }
    1728}