Commons IO example source code file (FilenameUtils.java)

This example Commons IO source code file (FilenameUtils.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons IO tags/keywords

arraylist, filenameutils, io, iocase, other_separator, stack, string, string, stringbuilder, system_separator, system_separator, unix_separator, unix_separator, util, windows_separator, windows_separator

The Commons IO FilenameUtils.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.io;

import java.io.File;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Stack;

/**
 * General filename and filepath manipulation utilities.
 * <p>
 * When dealing with filenames you can hit problems when moving from a Windows
 * based development machine to a Unix based production machine.
 * This class aims to help avoid those problems.
 * <p>
 * <b>NOTE: You may be able to avoid using this class entirely simply by
 * using JDK {@link java.io.File File} objects and the two argument constructor
 * {@link java.io.File#File(java.io.File, java.lang.String) File(File,String)}.
 * <p>
 * Most methods on this class are designed to work the same on both Unix and Windows.
 * Those that don't include 'System', 'Unix' or 'Windows' in their name.
 * <p>
 * Most methods recognise both separators (forward and back), and both
 * sets of prefixes. See the javadoc of each method for details.
 * <p>
 * This class defines six components within a filename
 * (example C:\dev\project\file.txt):
 * <ul>
 * <li>the prefix - C:\
 * <li>the path - dev\project\
 * <li>the full path - C:\dev\project\
 * <li>the name - file.txt
 * <li>the base name - file
 * <li>the extension - txt
 * </ul>
 * Note that this class works best if directory filenames end with a separator.
 * If you omit the last separator, it is impossible to determine if the filename
 * corresponds to a file or a directory. As a result, we have chosen to say
 * it corresponds to a file.
 * <p>
 * This class only supports Unix and Windows style names.
 * Prefixes are matched as follows:
 * <pre>
 * Windows:
 * a\b\c.txt           --> ""          --> relative
 * \a\b\c.txt          --> "\"         --> current drive absolute
 * C:a\b\c.txt         --> "C:"        --> drive relative
 * C:\a\b\c.txt        --> "C:\"       --> absolute
 * \\server\a\b\c.txt  --> "\\server\" --> UNC
 *
 * Unix:
 * a/b/c.txt           --> ""          --> relative
 * /a/b/c.txt          --> "/"         --> absolute
 * ~/a/b/c.txt         --> "~/"        --> current user
 * ~                   --> "~/"        --> current user (slash added)
 * ~user/a/b/c.txt     --> "~user/"    --> named user
 * ~user               --> "~user/"    --> named user (slash added)
 * </pre>
 * Both prefix styles are matched always, irrespective of the machine that you are
 * currently running on.
 * <p>
 * Origin of code: Excalibur, Alexandria, Tomcat, Commons-Utils.
 *
 * @author <a href="mailto:burton@relativity.yi.org">Kevin A. Burton
 * @author <a href="mailto:sanders@apache.org">Scott Sanders
 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall
 * @author <a href="mailto:Christoph.Reck@dlr.de">Christoph.Reck
 * @author <a href="mailto:peter@apache.org">Peter Donald
 * @author <a href="mailto:jefft@apache.org">Jeff Turner
 * @author Matthew Hawthorne
 * @author Martin Cooper
 * @author <a href="mailto:jeremias@apache.org">Jeremias Maerki
 * @author Stephen Colebourne
 * @version $Id: FilenameUtils.java 1004077 2010-10-04 00:58:42Z niallp $
 * @since Commons IO 1.1
 */
public class FilenameUtils {

    /**
     * The extension separator character.
     * @since Commons IO 1.4
     */
    public static final char EXTENSION_SEPARATOR = '.';

    /**
     * The extension separator String.
     * @since Commons IO 1.4
     */
    public static final String EXTENSION_SEPARATOR_STR = Character.toString(EXTENSION_SEPARATOR);

    /**
     * The Unix separator character.
     */
    private static final char UNIX_SEPARATOR = '/';

    /**
     * The Windows separator character.
     */
    private static final char WINDOWS_SEPARATOR = '\\';

    /**
     * The system separator character.
     */
    private static final char SYSTEM_SEPARATOR = File.separatorChar;

    /**
     * The separator character that is the opposite of the system separator.
     */
    private static final char OTHER_SEPARATOR;
    static {
        if (isSystemWindows()) {
            OTHER_SEPARATOR = UNIX_SEPARATOR;
        } else {
            OTHER_SEPARATOR = WINDOWS_SEPARATOR;
        }
    }

    /**
     * Instances should NOT be constructed in standard programming.
     */
    public FilenameUtils() {
        super();
    }

    //-----------------------------------------------------------------------
    /**
     * Determines if Windows file system is in use.
     * 
     * @return true if the system is Windows
     */
    static boolean isSystemWindows() {
        return SYSTEM_SEPARATOR == WINDOWS_SEPARATOR;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks if the character is a separator.
     * 
     * @param ch  the character to check
     * @return true if it is a separator character
     */
    private static boolean isSeparator(char ch) {
        return (ch == UNIX_SEPARATOR) || (ch == WINDOWS_SEPARATOR);
    }

    //-----------------------------------------------------------------------
    /**
     * Normalizes a path, removing double and single dot path steps.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format of the system.
     * <p>
     * A trailing slash will be retained.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo/
     * /foo/./              -->   /foo/
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar/
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo/
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar/
     * ~/../bar             -->   null
     * </pre>
     * (Note the file separator returned will be correct for Windows/Unix)
     *
     * @param filename  the filename to normalize, null returns null
     * @return the normalized filename, or null if invalid
     */
    public static String normalize(String filename) {
        return doNormalize(filename, SYSTEM_SEPARATOR, true);
    }
    /**
     * Normalizes a path, removing double and single dot path steps.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format specified.
     * <p>
     * A trailing slash will be retained.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo/
     * /foo/./              -->   /foo/
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar/
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo/
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar/
     * ~/../bar             -->   null
     * </pre>
     * The output will be the same on both Unix and Windows including
     * the separator character.
     *
     * @param filename  the filename to normalize, null returns null
     * @param unixSeparator <code>true if a unix separator should
     * be used or <code>false if a windows separator should be used.
     * @return the normalized filename, or null if invalid
     * @since Commons IO 2.0
     */
    public static String normalize(String filename, boolean unixSeparator) {
        char separator = (unixSeparator ? UNIX_SEPARATOR : WINDOWS_SEPARATOR);
        return doNormalize(filename, separator, true);
    }

    //-----------------------------------------------------------------------
    /**
     * Normalizes a path, removing double and single dot path steps,
     * and removing any final directory separator.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format of the system.
     * <p>
     * A trailing slash will be removed.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo//               -->   /foo
     * /foo/./              -->   /foo
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar
     * ~/../bar             -->   null
     * </pre>
     * (Note the file separator returned will be correct for Windows/Unix)
     *
     * @param filename  the filename to normalize, null returns null
     * @return the normalized filename, or null if invalid
     */
    public static String normalizeNoEndSeparator(String filename) {
        return doNormalize(filename, SYSTEM_SEPARATOR, false);
    }

    /**
     * Normalizes a path, removing double and single dot path steps,
     * and removing any final directory separator.
     * <p>
     * This method normalizes a path to a standard format.
     * The input may contain separators in either Unix or Windows format.
     * The output will contain separators in the format specified.
     * <p>
     * A trailing slash will be removed.
     * A double slash will be merged to a single slash (but UNC names are handled).
     * A single dot path segment will be removed.
     * A double dot will cause that path segment and the one before to be removed.
     * If the double dot has no parent path segment to work with, <code>null
     * is returned.
     * <p>
     * The output will be the same on both Unix and Windows including
     * the separator character.
     * <pre>
     * /foo//               -->   /foo
     * /foo/./              -->   /foo
     * /foo/../bar          -->   /bar
     * /foo/../bar/         -->   /bar
     * /foo/../bar/../baz   -->   /baz
     * //foo//./bar         -->   /foo/bar
     * /../                 -->   null
     * ../foo               -->   null
     * foo/bar/..           -->   foo
     * foo/../../bar        -->   null
     * foo/../bar           -->   bar
     * //server/foo/../bar  -->   //server/bar
     * //server/../bar      -->   null
     * C:\foo\..\bar        -->   C:\bar
     * C:\..\bar            -->   null
     * ~/foo/../bar/        -->   ~/bar
     * ~/../bar             -->   null
     * </pre>
     *
     * @param filename  the filename to normalize, null returns null
     * @param unixSeparator <code>true if a unix separator should
     * be used or <code>false if a windows separtor should be used.
     * @return the normalized filename, or null if invalid
     * @since Commons IO 2.0
     */
    public static String normalizeNoEndSeparator(String filename, boolean unixSeparator) {
         char separator = (unixSeparator ? UNIX_SEPARATOR : WINDOWS_SEPARATOR);
        return doNormalize(filename, separator, false);
    }

    /**
     * Internal method to perform the normalization.
     *
     * @param filename  the filename
     * @param separator The separator character to use
     * @param keepSeparator  true to keep the final separator
     * @return the normalized filename
     */
    private static String doNormalize(String filename, char separator, boolean keepSeparator) {
        if (filename == null) {
            return null;
        }
        int size = filename.length();
        if (size == 0) {
            return filename;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        
        char[] array = new char[size + 2];  // +1 for possible extra slash, +2 for arraycopy
        filename.getChars(0, filename.length(), array, 0);
        
        // fix separators throughout
        char otherSeparator = (separator == SYSTEM_SEPARATOR ? OTHER_SEPARATOR : SYSTEM_SEPARATOR);
        for (int i = 0; i < array.length; i++) {
            if (array[i] == otherSeparator) {
                array[i] = separator;
            }
        }
        
        // add extra separator on the end to simplify code below
        boolean lastIsDirectory = true;
        if (array[size - 1] != separator) {
            array[size++] = separator;
            lastIsDirectory = false;
        }
        
        // adjoining slashes
        for (int i = prefix + 1; i < size; i++) {
            if (array[i] == separator && array[i - 1] == separator) {
                System.arraycopy(array, i, array, i - 1, size - i);
                size--;
                i--;
            }
        }
        
        // dot slash
        for (int i = prefix + 1; i < size; i++) {
            if (array[i] == separator && array[i - 1] == '.' &&
                    (i == prefix + 1 || array[i - 2] == separator)) {
                if (i == size - 1) {
                    lastIsDirectory = true;
                }
                System.arraycopy(array, i + 1, array, i - 1, size - i);
                size -=2;
                i--;
            }
        }
        
        // double dot slash
        outer:
        for (int i = prefix + 2; i < size; i++) {
            if (array[i] == separator && array[i - 1] == '.' && array[i - 2] == '.' &&
                    (i == prefix + 2 || array[i - 3] == separator)) {
                if (i == prefix + 2) {
                    return null;
                }
                if (i == size - 1) {
                    lastIsDirectory = true;
                }
                int j;
                for (j = i - 4 ; j >= prefix; j--) {
                    if (array[j] == separator) {
                        // remove b/../ from a/b/../c
                        System.arraycopy(array, i + 1, array, j + 1, size - i);
                        size -= (i - j);
                        i = j + 1;
                        continue outer;
                    }
                }
                // remove a/../ from a/../c
                System.arraycopy(array, i + 1, array, prefix, size - i);
                size -= (i + 1 - prefix);
                i = prefix + 1;
            }
        }
        
        if (size <= 0) {  // should never be less than 0
            return "";
        }
        if (size <= prefix) {  // should never be less than prefix
            return new String(array, 0, size);
        }
        if (lastIsDirectory && keepSeparator) {
            return new String(array, 0, size);  // keep trailing separator
        }
        return new String(array, 0, size - 1);  // lose trailing separator
    }

    //-----------------------------------------------------------------------
    /**
     * Concatenates a filename to a base path using normal command line style rules.
     * <p>
     * The effect is equivalent to resultant directory after changing
     * directory to the first argument, followed by changing directory to
     * the second argument.
     * <p>
     * The first argument is the base path, the second is the path to concatenate.
     * The returned path is always normalized via {@link #normalize(String)},
     * thus <code>.. is handled.
     * <p>
     * If <code>pathToAdd is absolute (has an absolute prefix), then
     * it will be normalized and returned.
     * Otherwise, the paths will be joined, normalized and returned.
     * <p>
     * The output will be the same on both Unix and Windows except
     * for the separator character.
     * <pre>
     * /foo/ + bar          -->   /foo/bar
     * /foo + bar           -->   /foo/bar
     * /foo + /bar          -->   /bar
     * /foo + C:/bar        -->   C:/bar
     * /foo + C:bar         -->   C:bar (*)
     * /foo/a/ + ../bar     -->   foo/bar
     * /foo/ + ../../bar    -->   null
     * /foo/ + /bar         -->   /bar
     * /foo/.. + /bar       -->   /bar
     * /foo + bar/c.txt     -->   /foo/bar/c.txt
     * /foo/c.txt + bar     -->   /foo/c.txt/bar (!)
     * </pre>
     * (*) Note that the Windows relative drive prefix is unreliable when
     * used with this method.
     * (!) Note that the first parameter must be a path. If it ends with a name, then
     * the name will be built into the concatenated path. If this might be a problem,
     * use {@link #getFullPath(String)} on the base path argument.
     *
     * @param basePath  the base path to attach to, always treated as a path
     * @param fullFilenameToAdd  the filename (or path) to attach to the base
     * @return the concatenated path, or null if invalid
     */
    public static String concat(String basePath, String fullFilenameToAdd) {
        int prefix = getPrefixLength(fullFilenameToAdd);
        if (prefix < 0) {
            return null;
        }
        if (prefix > 0) {
            return normalize(fullFilenameToAdd);
        }
        if (basePath == null) {
            return null;
        }
        int len = basePath.length();
        if (len == 0) {
            return normalize(fullFilenameToAdd);
        }
        char ch = basePath.charAt(len - 1);
        if (isSeparator(ch)) {
            return normalize(basePath + fullFilenameToAdd);
        } else {
            return normalize(basePath + '/' + fullFilenameToAdd);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Converts all separators to the Unix separator of forward slash.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToUnix(String path) {
        if (path == null || path.indexOf(WINDOWS_SEPARATOR) == -1) {
            return path;
        }
        return path.replace(WINDOWS_SEPARATOR, UNIX_SEPARATOR);
    }

    /**
     * Converts all separators to the Windows separator of backslash.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToWindows(String path) {
        if (path == null || path.indexOf(UNIX_SEPARATOR) == -1) {
            return path;
        }
        return path.replace(UNIX_SEPARATOR, WINDOWS_SEPARATOR);
    }

    /**
     * Converts all separators to the system separator.
     * 
     * @param path  the path to be changed, null ignored
     * @return the updated path
     */
    public static String separatorsToSystem(String path) {
        if (path == null) {
            return null;
        }
        if (isSystemWindows()) {
            return separatorsToWindows(path);
        } else {
            return separatorsToUnix(path);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the length of the filename prefix, such as <code>C:/ or ~/.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * <p>
     * The prefix length includes the first slash in the full filename
     * if applicable. Thus, it is possible that the length returned is greater
     * than the length of the input string.
     * <pre>
     * Windows:
     * a\b\c.txt           --> ""          --> relative
     * \a\b\c.txt          --> "\"         --> current drive absolute
     * C:a\b\c.txt         --> "C:"        --> drive relative
     * C:\a\b\c.txt        --> "C:\"       --> absolute
     * \\server\a\b\c.txt  --> "\\server\" --> UNC
     *
     * Unix:
     * a/b/c.txt           --> ""          --> relative
     * /a/b/c.txt          --> "/"         --> absolute
     * ~/a/b/c.txt         --> "~/"        --> current user
     * ~                   --> "~/"        --> current user (slash added)
     * ~user/a/b/c.txt     --> "~user/"    --> named user
     * ~user               --> "~user/"    --> named user (slash added)
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * ie. both Unix and Windows prefixes are matched regardless.
     *
     * @param filename  the filename to find the prefix in, null returns -1
     * @return the length of the prefix, -1 if invalid or null
     */
    public static int getPrefixLength(String filename) {
        if (filename == null) {
            return -1;
        }
        int len = filename.length();
        if (len == 0) {
            return 0;
        }
        char ch0 = filename.charAt(0);
        if (ch0 == ':') {
            return -1;
        }
        if (len == 1) {
            if (ch0 == '~') {
                return 2;  // return a length greater than the input
            }
            return (isSeparator(ch0) ? 1 : 0);
        } else {
            if (ch0 == '~') {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 1);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 1);
                if (posUnix == -1 && posWin == -1) {
                    return len + 1;  // return a length greater than the input
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            }
            char ch1 = filename.charAt(1);
            if (ch1 == ':') {
                ch0 = Character.toUpperCase(ch0);
                if (ch0 >= 'A' && ch0 <= 'Z') {
                    if (len == 2 || isSeparator(filename.charAt(2)) == false) {
                        return 2;
                    }
                    return 3;
                }
                return -1;
                
            } else if (isSeparator(ch0) && isSeparator(ch1)) {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 2);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 2);
                if ((posUnix == -1 && posWin == -1) || posUnix == 2 || posWin == 2) {
                    return -1;
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            } else {
                return (isSeparator(ch0) ? 1 : 0);
            }
        }
    }

    /**
     * Returns the index of the last directory separator character.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The position of the last forward or backslash is returned.
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * 
     * @param filename  the filename to find the last path separator in, null returns -1
     * @return the index of the last separator character, or -1 if there
     * is no such character
     */
    public static int indexOfLastSeparator(String filename) {
        if (filename == null) {
            return -1;
        }
        int lastUnixPos = filename.lastIndexOf(UNIX_SEPARATOR);
        int lastWindowsPos = filename.lastIndexOf(WINDOWS_SEPARATOR);
        return Math.max(lastUnixPos, lastWindowsPos);
    }

    /**
     * Returns the index of the last extension separator character, which is a dot.
     * <p>
     * This method also checks that there is no directory separator after the last dot.
     * To do this it uses {@link #indexOfLastSeparator(String)} which will
     * handle a file in either Unix or Windows format.
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * 
     * @param filename  the filename to find the last path separator in, null returns -1
     * @return the index of the last separator character, or -1 if there
     * is no such character
     */
    public static int indexOfExtension(String filename) {
        if (filename == null) {
            return -1;
        }
        int extensionPos = filename.lastIndexOf(EXTENSION_SEPARATOR);
        int lastSeparator = indexOfLastSeparator(filename);
        return (lastSeparator > extensionPos ? -1 : extensionPos);
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the prefix from a full filename, such as <code>C:/
     * or <code>~/.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The prefix includes the first slash in the full filename where applicable.
     * <pre>
     * Windows:
     * a\b\c.txt           --> ""          --> relative
     * \a\b\c.txt          --> "\"         --> current drive absolute
     * C:a\b\c.txt         --> "C:"        --> drive relative
     * C:\a\b\c.txt        --> "C:\"       --> absolute
     * \\server\a\b\c.txt  --> "\\server\" --> UNC
     *
     * Unix:
     * a/b/c.txt           --> ""          --> relative
     * /a/b/c.txt          --> "/"         --> absolute
     * ~/a/b/c.txt         --> "~/"        --> current user
     * ~                   --> "~/"        --> current user (slash added)
     * ~user/a/b/c.txt     --> "~user/"    --> named user
     * ~user               --> "~user/"    --> named user (slash added)
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * ie. both Unix and Windows prefixes are matched regardless.
     *
     * @param filename  the filename to query, null returns null
     * @return the prefix of the file, null if invalid
     */
    public static String getPrefix(String filename) {
        if (filename == null) {
            return null;
        }
        int len = getPrefixLength(filename);
        if (len < 0) {
            return null;
        }
        if (len > filename.length()) {
            return filename + UNIX_SEPARATOR;  // we know this only happens for unix
        }
        return filename.substring(0, len);
    }

    /**
     * Gets the path from a full filename, which excludes the prefix.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before and
     * including the last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> a\b\
     * ~/a/b/c.txt  --> a/b/
     * a.txt        --> ""
     * a/b/c        --> a/b/
     * a/b/c/       --> a/b/c/
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * <p>
     * This method drops the prefix from the result.
     * See {@link #getFullPath(String)} for the method that retains the prefix.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getPath(String filename) {
        return doGetPath(filename, 1);
    }

    /**
     * Gets the path from a full filename, which excludes the prefix, and
     * also excluding the final directory separator.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before the
     * last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> a\b
     * ~/a/b/c.txt  --> a/b
     * a.txt        --> ""
     * a/b/c        --> a/b
     * a/b/c/       --> a/b/c
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     * <p>
     * This method drops the prefix from the result.
     * See {@link #getFullPathNoEndSeparator(String)} for the method that retains the prefix.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getPathNoEndSeparator(String filename) {
        return doGetPath(filename, 0);
    }

    /**
     * Does the work of getting the path.
     * 
     * @param filename  the filename
     * @param separatorAdd  0 to omit the end separator, 1 to return it
     * @return the path
     */
    private static String doGetPath(String filename, int separatorAdd) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        int index = indexOfLastSeparator(filename);
        int endIndex = index+separatorAdd;
        if (prefix >= filename.length() || index < 0 || prefix >= endIndex) {
            return "";
        }
        return filename.substring(prefix, endIndex);
    }

    /**
     * Gets the full path from a full filename, which is the prefix + path.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before and
     * including the last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> C:\a\b\
     * ~/a/b/c.txt  --> ~/a/b/
     * a.txt        --> ""
     * a/b/c        --> a/b/
     * a/b/c/       --> a/b/c/
     * C:           --> C:
     * C:\          --> C:\
     * ~            --> ~/
     * ~/           --> ~/
     * ~user        --> ~user/
     * ~user/       --> ~user/
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getFullPath(String filename) {
        return doGetFullPath(filename, true);
    }

    /**
     * Gets the full path from a full filename, which is the prefix + path,
     * and also excluding the final directory separator.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The method is entirely text based, and returns the text before the
     * last forward or backslash.
     * <pre>
     * C:\a\b\c.txt --> C:\a\b
     * ~/a/b/c.txt  --> ~/a/b
     * a.txt        --> ""
     * a/b/c        --> a/b
     * a/b/c/       --> a/b/c
     * C:           --> C:
     * C:\          --> C:\
     * ~            --> ~
     * ~/           --> ~
     * ~user        --> ~user
     * ~user/       --> ~user
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the path of the file, an empty string if none exists, null if invalid
     */
    public static String getFullPathNoEndSeparator(String filename) {
        return doGetFullPath(filename, false);
    }

    /**
     * Does the work of getting the path.
     * 
     * @param filename  the filename
     * @param includeSeparator  true to include the end separator
     * @return the path
     */
    private static String doGetFullPath(String filename, boolean includeSeparator) {
        if (filename == null) {
            return null;
        }
        int prefix = getPrefixLength(filename);
        if (prefix < 0) {
            return null;
        }
        if (prefix >= filename.length()) {
            if (includeSeparator) {
                return getPrefix(filename);  // add end slash if necessary
            } else {
                return filename;
            }
        }
        int index = indexOfLastSeparator(filename);
        if (index < 0) {
            return filename.substring(0, prefix);
        }
        int end = index + (includeSeparator ?  1 : 0);
        if (end == 0) {
            end++;
        }
        return filename.substring(0, end);
    }

    /**
     * Gets the name minus the path from a full filename.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The text after the last forward or backslash is returned.
     * <pre>
     * a/b/c.txt --> c.txt
     * a.txt     --> a.txt
     * a/b/c     --> c
     * a/b/c/    --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the name of the file without the path, or an empty string if none exists
     */
    public static String getName(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfLastSeparator(filename);
        return filename.substring(index + 1);
    }

    /**
     * Gets the base name, minus the full path and extension, from a full filename.
     * <p>
     * This method will handle a file in either Unix or Windows format.
     * The text after the last forward or backslash and before the last dot is returned.
     * <pre>
     * a/b/c.txt --> c
     * a.txt     --> a
     * a/b/c     --> c
     * a/b/c/    --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the name of the file without the path, or an empty string if none exists
     */
    public static String getBaseName(String filename) {
        return removeExtension(getName(filename));
    }

    /**
     * Gets the extension of a filename.
     * <p>
     * This method returns the textual part of the filename after the last dot.
     * There must be no directory separator after the dot.
     * <pre>
     * foo.txt      --> "txt"
     * a/b/c.jpg    --> "jpg"
     * a/b.txt/c    --> ""
     * a/b/c        --> ""
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename the filename to retrieve the extension of.
     * @return the extension of the file or an empty string if none exists or <code>null
     * if the filename is <code>null.
     */
    public static String getExtension(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfExtension(filename);
        if (index == -1) {
            return "";
        } else {
            return filename.substring(index + 1);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Removes the extension from a filename.
     * <p>
     * This method returns the textual part of the filename before the last dot.
     * There must be no directory separator after the dot.
     * <pre>
     * foo.txt    --> foo
     * a\b\c.jpg  --> a\b\c
     * a\b\c      --> a\b\c
     * a.b\c      --> a.b\c
     * </pre>
     * <p>
     * The output will be the same irrespective of the machine that the code is running on.
     *
     * @param filename  the filename to query, null returns null
     * @return the filename minus the extension
     */
    public static String removeExtension(String filename) {
        if (filename == null) {
            return null;
        }
        int index = indexOfExtension(filename);
        if (index == -1) {
            return filename;
        } else {
            return filename.substring(0, index);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether two filenames are equal exactly.
     * <p>
     * No processing is performed on the filenames other than comparison,
     * thus this is merely a null-safe case-sensitive equals.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SENSITIVE
     */
    public static boolean equals(String filename1, String filename2) {
        return equals(filename1, filename2, false, IOCase.SENSITIVE);
    }

    /**
     * Checks whether two filenames are equal using the case rules of the system.
     * <p>
     * No processing is performed on the filenames other than comparison.
     * The check is case-sensitive on Unix and case-insensitive on Windows.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SYSTEM
     */
    public static boolean equalsOnSystem(String filename1, String filename2) {
        return equals(filename1, filename2, false, IOCase.SYSTEM);
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether two filenames are equal after both have been normalized.
     * <p>
     * Both filenames are first passed to {@link #normalize(String)}.
     * The check is then performed in a case-sensitive manner.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SENSITIVE
     */
    public static boolean equalsNormalized(String filename1, String filename2) {
        return equals(filename1, filename2, true, IOCase.SENSITIVE);
    }

    /**
     * Checks whether two filenames are equal after both have been normalized
     * and using the case rules of the system.
     * <p>
     * Both filenames are first passed to {@link #normalize(String)}.
     * The check is then performed case-sensitive on Unix and
     * case-insensitive on Windows.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @return true if the filenames are equal, null equals null
     * @see IOCase#SYSTEM
     */
    public static boolean equalsNormalizedOnSystem(String filename1, String filename2) {
        return equals(filename1, filename2, true, IOCase.SYSTEM);
    }

    /**
     * Checks whether two filenames are equal, optionally normalizing and providing
     * control over the case-sensitivity.
     *
     * @param filename1  the first filename to query, may be null
     * @param filename2  the second filename to query, may be null
     * @param normalized  whether to normalize the filenames
     * @param caseSensitivity  what case sensitivity rule to use, null means case-sensitive
     * @return true if the filenames are equal, null equals null
     * @since Commons IO 1.3
     */
    public static boolean equals(
            String filename1, String filename2,
            boolean normalized, IOCase caseSensitivity) {
        
        if (filename1 == null || filename2 == null) {
            return (filename1 == null && filename2 == null);
        }
        if (normalized) {
            filename1 = normalize(filename1);
            filename2 = normalize(filename2);
            if (filename1 == null || filename2 == null) {
                throw new NullPointerException(
                    "Error normalizing one or both of the file names");
            }
        }
        if (caseSensitivity == null) {
            caseSensitivity = IOCase.SENSITIVE;
        }
        return caseSensitivity.checkEquals(filename1, filename2);
    }

    //-----------------------------------------------------------------------
    /**
     * Checks whether the extension of the filename is that specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extension  the extension to check for, null or empty checks for no extension
     * @return true if the filename has the specified extension
     */
    public static boolean isExtension(String filename, String extension) {
        if (filename == null) {
            return false;
        }
        if (extension == null || extension.length() == 0) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        return fileExt.equals(extension);
    }

    /**
     * Checks whether the extension of the filename is one of those specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extensions  the extensions to check for, null checks for no extension
     * @return true if the filename is one of the extensions
     */
    public static boolean isExtension(String filename, String[] extensions) {
        if (filename == null) {
            return false;
        }
        if (extensions == null || extensions.length == 0) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        for (String extension : extensions) {
            if (fileExt.equals(extension)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Checks whether the extension of the filename is one of those specified.
     * <p>
     * This method obtains the extension as the textual part of the filename
     * after the last dot. There must be no directory separator after the dot.
     * The extension check is case-sensitive on all platforms.
     *
     * @param filename  the filename to query, null returns false
     * @param extensions  the extensions to check for, null checks for no extension
     * @return true if the filename is one of the extensions
     */
    public static boolean isExtension(String filename, Collection<String> extensions) {
        if (filename == null) {
            return false;
        }
        if (extensions == null || extensions.isEmpty()) {
            return (indexOfExtension(filename) == -1);
        }
        String fileExt = getExtension(filename);
        for (String extension : extensions) {
            if (fileExt.equals(extension)) {
                return true;
            }
        }
        return false;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks a filename to see if it matches the specified wildcard matcher,
     * always testing case-sensitive.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * This is the same as often found on Dos/Unix command lines.
     * The check is case-sensitive always.
     * <pre>
     * wildcardMatch("c.txt", "*.txt")      --> true
     * wildcardMatch("c.txt", "*.jpg")      --> false
     * wildcardMatch("a/b/c.txt", "a/b/*")  --> true
     * wildcardMatch("c.txt", "*.???")      --> true
     * wildcardMatch("c.txt", "*.????")     --> false
     * </pre>
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @return true if the filename matches the wilcard string
     * @see IOCase#SENSITIVE
     */
    public static boolean wildcardMatch(String filename, String wildcardMatcher) {
        return wildcardMatch(filename, wildcardMatcher, IOCase.SENSITIVE);
    }

    /**
     * Checks a filename to see if it matches the specified wildcard matcher
     * using the case rules of the system.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * This is the same as often found on Dos/Unix command lines.
     * The check is case-sensitive on Unix and case-insensitive on Windows.
     * <pre>
     * wildcardMatch("c.txt", "*.txt")      --> true
     * wildcardMatch("c.txt", "*.jpg")      --> false
     * wildcardMatch("a/b/c.txt", "a/b/*")  --> true
     * wildcardMatch("c.txt", "*.???")      --> true
     * wildcardMatch("c.txt", "*.????")     --> false
     * </pre>
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @return true if the filename matches the wilcard string
     * @see IOCase#SYSTEM
     */
    public static boolean wildcardMatchOnSystem(String filename, String wildcardMatcher) {
        return wildcardMatch(filename, wildcardMatcher, IOCase.SYSTEM);
    }

    /**
     * Checks a filename to see if it matches the specified wildcard matcher
     * allowing control over case-sensitivity.
     * <p>
     * The wildcard matcher uses the characters '?' and '*' to represent a
     * single or multiple (zero or more) wildcard characters.
     * N.B. the sequence "*?" does not work properly at present in match strings.
     * 
     * @param filename  the filename to match on
     * @param wildcardMatcher  the wildcard string to match against
     * @param caseSensitivity  what case sensitivity rule to use, null means case-sensitive
     * @return true if the filename matches the wilcard string
     * @since Commons IO 1.3
     */
    public static boolean wildcardMatch(String filename, String wildcardMatcher, IOCase caseSensitivity) {
        if (filename == null && wildcardMatcher == null) {
            return true;
        }
        if (filename == null || wildcardMatcher == null) {
            return false;
        }
        if (caseSensitivity == null) {
            caseSensitivity = IOCase.SENSITIVE;
        }
        String[] wcs = splitOnTokens(wildcardMatcher);
        boolean anyChars = false;
        int textIdx = 0;
        int wcsIdx = 0;
        Stack<int[]> backtrack = new Stack();
        
        // loop around a backtrack stack, to handle complex * matching
        do {
            if (backtrack.size() > 0) {
                int[] array = backtrack.pop();
                wcsIdx = array[0];
                textIdx = array[1];
                anyChars = true;
            }
            
            // loop whilst tokens and text left to process
            while (wcsIdx < wcs.length) {
      
                if (wcs[wcsIdx].equals("?")) {
                    // ? so move to next text char
                    textIdx++;
                    if (textIdx > filename.length()) {
                        break;
                    }
                    anyChars = false;
                    
                } else if (wcs[wcsIdx].equals("*")) {
                    // set any chars status
                    anyChars = true;
                    if (wcsIdx == wcs.length - 1) {
                        textIdx = filename.length();
                    }
                    
                } else {
                    // matching text token
                    if (anyChars) {
                        // any chars then try to locate text token
                        textIdx = caseSensitivity.checkIndexOf(filename, textIdx, wcs[wcsIdx]);
                        if (textIdx == -1) {
                            // token not found
                            break;
                        }
                        int repeat = caseSensitivity.checkIndexOf(filename, textIdx + 1, wcs[wcsIdx]);
                        if (repeat >= 0) {
                            backtrack.push(new int[] {wcsIdx, repeat});
                        }
                    } else {
                        // matching from current position
                        if (!caseSensitivity.checkRegionMatches(filename, textIdx, wcs[wcsIdx])) {
                            // couldnt match token
                            break;
                        }
                    }
      
                    // matched text token, move text index to end of matched token
                    textIdx += wcs[wcsIdx].length();
                    anyChars = false;
                }
      
                wcsIdx++;
            }
            
            // full match
            if (wcsIdx == wcs.length && textIdx == filename.length()) {
                return true;
            }
            
        } while (backtrack.size() > 0);
  
        return false;
    }

    /**
     * Splits a string into a number of tokens.
     * The text is split by '?' and '*'.
     * Where multiple '*' occur consecutively they are collapsed into a single '*'.
     * 
     * @param text  the text to split
     * @return the array of tokens, never null
     */
    static String[] splitOnTokens(String text) {
        // used by wildcardMatch
        // package level so a unit test may run on this
        
        if (text.indexOf('?') == -1 && text.indexOf('*') == -1) {
            return new String[] { text };
        }

        char[] array = text.toCharArray();
        ArrayList<String> list = new ArrayList();
        StringBuilder buffer = new StringBuilder();
        for (int i = 0; i < array.length; i++) {
            if (array[i] == '?' || array[i] == '*') {
                if (buffer.length() != 0) {
                    list.add(buffer.toString());
                    buffer.setLength(0);
                }
                if (array[i] == '?') {
                    list.add("?");
                } else if (list.size() == 0 ||
                        (i > 0 && list.get(list.size() - 1).equals("*") == false)) {
                    list.add("*");
                }
            } else {
                buffer.append(array[i]);
            }
        }
        if (buffer.length() != 0) {
            list.add(buffer.toString());
        }

        return list.toArray( new String[ list.size() ] );
    }

}