    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     */
    017    package org.apache.commons.io.comparator;
    018
    019    import java.io.File;
    020    import java.io.Serializable;
    021    import java.util.Comparator;
    022
    023    import org.apache.commons.io.FilenameUtils;
    024    import org.apache.commons.io.IOCase;
    025
    026    /**
    027     * Compare the file name <b>extensions</b> 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 dependant 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     * Example of a <i>case-sensitive</i> file extension sort using the
    037     * {@link #EXTENSION_COMPARATOR} singleton instance:
    038     * <pre>
    039     *       List&lt;File&gt; list = ...
    040     *       ExtensionFileComparator.EXTENSION_COMPARATOR.sort(list);
    041     * </pre>
    042     * <p>
    043     * Example of a <i>reverse case-insensitive</i> file extension sort using the
    044     * {@link #EXTENSION_INSENSITIVE_REVERSE} singleton instance:
    045     * <pre>
    046     *       File[] array = ...
    047     *       ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE.sort(array);
    048     * </pre>
    049     * <p>
    050     *
    051     * @version $Revision: 1003216 $ $Date: 2010-09-30 20:39:21 +0100 (Thu, 30 Sep 2010) $
    052     * @since Commons IO 1.4
    053     */
    054    public class ExtensionFileComparator extends AbstractFileComparator implements Serializable {
    055
    056        /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    057        public static final Comparator<File> EXTENSION_COMPARATOR = new ExtensionFileComparator();
    058
    059        /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    060        public static final Comparator<File> EXTENSION_REVERSE = new ReverseComparator(EXTENSION_COMPARATOR);
    061
    062        /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    063        public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR
    064                                                    = new ExtensionFileComparator(IOCase.INSENSITIVE);
    065
    066        /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    067        public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE
    068                                                    = new ReverseComparator(EXTENSION_INSENSITIVE_COMPARATOR);
    069
    070        /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
    071        public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
    072
    073        /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
    074        public static final Comparator<File> EXTENSION_SYSTEM_REVERSE = new ReverseComparator(EXTENSION_SYSTEM_COMPARATOR);
    075
    076        /** Whether the comparison is case sensitive. */
    077        private final IOCase caseSensitivity;
    078
    079        /**
    080         * Construct a case sensitive file extension comparator instance.
    081         */
    082        public ExtensionFileComparator() {
    083            this.caseSensitivity = IOCase.SENSITIVE;
    084        }
    085
    086        /**
    087         * Construct a file extension comparator instance with the specified case-sensitivity.
    088         *
    089         * @param caseSensitivity how to handle case sensitivity, null means case-sensitive
    090         */
    091        public ExtensionFileComparator(IOCase caseSensitivity) {
    092            this.caseSensitivity = caseSensitivity == null ? IOCase.SENSITIVE : caseSensitivity;
    093        }
    094
    095        /**
    096         * Compare the extensions of two files the specified case sensitivity.
    097         *
    098         * @param file1 The first file to compare
    099         * @param file2 The second file to compare
    100         * @return a negative value if the first file's extension
    101         * is less than the second, zero if the extensions are the
    102         * same and a positive value if the first files extension
    103         * is greater than the second file.
    104         *
    105         */
    106        public int compare(File file1, File file2) {
    107            String suffix1 = FilenameUtils.getExtension(file1.getName());
    108            String suffix2 = FilenameUtils.getExtension(file2.getName());
    109            return caseSensitivity.checkCompareTo(suffix1, suffix2);
    110        }
    111
    112        /**
    113         * String representation of this file comparator.
    114         *
    115         * @return String representation of this file comparator
    116         */
    117        @Override
    118        public String toString() {
    119            return super.toString() + "[caseSensitivity=" + caseSensitivity + "]";
    120        }
    121    }