    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 *      https://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.comparator;
    018
    019import java.io.File;
    020import java.io.Serializable;
    021import java.util.Comparator;
    022
    023import org.apache.commons.io.FilenameUtils;
    024import org.apache.commons.io.IOCase;
    025
    026/**
    027 * Compare the file name <strong>extensions</strong> for order
    028 * (see {@link FilenameUtils#getExtension(String)}).
    029 * <p>
    030 * This comparator can be used to sort lists or arrays of files
    031 * by their file extension either in a case-sensitive, case-insensitive or
    032 * system dependent case-sensitive way. A number of singleton instances
    033 * are provided for the various case sensitivity options (using {@link IOCase})
    034 * and the reverse of those options.
    035 * </p>
    036 * <p>
    037 * Example of a <em>case-sensitive</em> file extension sort using the
    038 * {@link #EXTENSION_COMPARATOR} singleton instance:
    039 * </p>
    040 * <pre>
    041 *       List&lt;File&gt; list = ...
    042 *       ((AbstractFileComparator) ExtensionFileComparator.EXTENSION_COMPARATOR).sort(list);
    043 * </pre>
    044 * <p>
    045 * Example of a <em>reverse case-insensitive</em> file extension sort using the
    046 * {@link #EXTENSION_INSENSITIVE_REVERSE} singleton instance:
    047 * </p>
    048 * <pre>
    049 *       File[] array = ...
    050 *       ((AbstractFileComparator) ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE).sort(array);
    051 * </pre>
    052 * <h2>Deprecating Serialization</h2>
    053 * <p>
    054 * <em>Serialization is deprecated and will be removed in 3.0.</em>
    055 * </p>
    056 *
    057 * @since 1.4
    058 */
    059public class ExtensionFileComparator extends AbstractFileComparator implements Serializable {
    060
    061    private static final long serialVersionUID = 1928235200184222815L;
    062
    063    /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    064    public static final Comparator<File> EXTENSION_COMPARATOR = new ExtensionFileComparator();
    065
    066    /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    067    public static final Comparator<File> EXTENSION_REVERSE = new ReverseFileComparator(EXTENSION_COMPARATOR);
    068
    069    /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    070    public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR
    071                                                = new ExtensionFileComparator(IOCase.INSENSITIVE);
    072
    073    /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    074    public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE
    075                                                = new ReverseFileComparator(EXTENSION_INSENSITIVE_COMPARATOR);
    076
    077    /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
    078    public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
    079
    080    /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
    081    public static final Comparator<File> EXTENSION_SYSTEM_REVERSE = new ReverseFileComparator(EXTENSION_SYSTEM_COMPARATOR);
    082
    083    /** Whether the comparison is case-sensitive. */
    084    private final IOCase ioCase;
    085
    086    /**
    087     * Constructs a case-sensitive file extension comparator instance.
    088     */
    089    public ExtensionFileComparator() {
    090        this.ioCase = IOCase.SENSITIVE;
    091    }
    092
    093    /**
    094     * Constructs a file extension comparator instance with the specified case-sensitivity.
    095     *
    096     * @param ioCase how to handle case sensitivity, null means case-sensitive.
    097     */
    098    public ExtensionFileComparator(final IOCase ioCase) {
    099        this.ioCase = IOCase.value(ioCase, IOCase.SENSITIVE);
    100    }
    101
    102    /**
    103     * Compares the extensions of two files the specified case sensitivity.
    104     *
    105     * @param file1 The first file to compare.
    106     * @param file2 The second file to compare.
    107     * @return a negative value if the first file's extension
    108     * is less than the second, zero if the extensions are the
    109     * same and a positive value if the first files extension
    110     * is greater than the second file.
    111     */
    112    @Override
    113    public int compare(final File file1, final File file2) {
    114        final String suffix1 = FilenameUtils.getExtension(file1.getName());
    115        final String suffix2 = FilenameUtils.getExtension(file2.getName());
    116        return ioCase.checkCompareTo(suffix1, suffix2);
    117    }
    118
    119    /**
    120     * String representation of this file comparator.
    121     *
    122     * @return String representation of this file comparator.
    123     */
    124    @Override
    125    public String toString() {
    126        return super.toString() + "[ioCase=" + ioCase + "]";
    127    }
    128}