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     *       Collections.sort(list, ExtensionFileComparator.EXTENSION_COMPARATOR);
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     *       Arrays.sort(array, ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE);
048     * </pre>
049     * <p>
050     *
051     * @version $Revision: 609243 $ $Date: 2008-01-06 00:30:42 +0000 (Sun, 06 Jan 2008) $
052     * @since Commons IO 1.4
053     */
054    public class ExtensionFileComparator implements Comparator, Serializable {
055    
056        /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
057        public static final Comparator EXTENSION_COMPARATOR = new ExtensionFileComparator();
058    
059        /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
060        public static final Comparator EXTENSION_REVERSE = new ReverseComparator(EXTENSION_COMPARATOR);
061    
062        /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
063        public static final Comparator EXTENSION_INSENSITIVE_COMPARATOR = new ExtensionFileComparator(IOCase.INSENSITIVE);
064    
065        /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
066        public static final Comparator EXTENSION_INSENSITIVE_REVERSE
067                                                    = new ReverseComparator(EXTENSION_INSENSITIVE_COMPARATOR);
068    
069        /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
070        public static final Comparator EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
071    
072        /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
073        public static final Comparator EXTENSION_SYSTEM_REVERSE = new ReverseComparator(EXTENSION_SYSTEM_COMPARATOR);
074    
075        /** Whether the comparison is case sensitive. */
076        private final IOCase caseSensitivity;
077    
078        /**
079         * Construct a case sensitive file extension comparator instance.
080         */
081        public ExtensionFileComparator() {
082            this.caseSensitivity = IOCase.SENSITIVE;
083        }
084    
085        /**
086         * Construct a file extension comparator instance with the specified case-sensitivity.
087         *
088         * @param caseSensitivity how to handle case sensitivity, null means case-sensitive
089         */
090        public ExtensionFileComparator(IOCase caseSensitivity) {
091            this.caseSensitivity = caseSensitivity == null ? IOCase.SENSITIVE : caseSensitivity;
092        }
093    
094        /**
095         * Compare the extensions of two files the specified case sensitivity.
096         * 
097         * @param obj1 The first file to compare
098         * @param obj2 The second file to compare
099         * @return a negative value if the first file's extension
100         * is less than the second, zero if the extensions are the
101         * same and a positive value if the first files extension
102         * is greater than the second file.
103         * 
104         */
105        public int compare(Object obj1, Object obj2) {
106            File file1 = (File)obj1;
107            File file2 = (File)obj2;
108            String suffix1 = FilenameUtils.getExtension(file1.getName());
109            String suffix2 = FilenameUtils.getExtension(file2.getName());
110            return caseSensitivity.checkCompareTo(suffix1, suffix2);
111        }
112    }