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      1 /*
      2  * Licensed to the Apache Software Foundation (ASF) under one or more
      3  * contributor license agreements.  See the NOTICE file distributed with
      4  * this work for additional information regarding copyright ownership.
      5  * The ASF licenses this file to You under the Apache License, Version 2.0
      6  * (the "License"); you may not use this file except in compliance with
      7  * the License.  You may obtain a copy of the License at
      8  *
      9  *      http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  * Unless required by applicable law or agreed to in writing, software
     12  * distributed under the License is distributed on an "AS IS" BASIS,
     13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  * See the License for the specific language governing permissions and
     15  * limitations under the License.
     16  */
     17 package org.apache.commons.io.comparator;
     18 
     19 import java.io.File;
     20 import java.io.Serializable;
     21 import java.util.Comparator;
     22 
     23 import org.apache.commons.io.FilenameUtils;
     24 import org.apache.commons.io.IOCase;
     25 
     26 /**
     27  * Compare the file name <b>extensions</b> for order
     28  * (see {@link FilenameUtils#getExtension(String)}).
     29  * <p>
     30  * This comparator can be used to sort lists or arrays of files
     31  * by their file extension either in a case-sensitive, case-insensitive or
     32  * system dependant case sensitive way. A number of singleton instances
     33  * are provided for the various case sensitivity options (using {@link IOCase})
     34  * and the reverse of those options.
     35  * <p>
     36  * Example of a <i>case-sensitive</i> file extension sort using the
     37  * {@link #EXTENSION_COMPARATOR} singleton instance:
     38  * <pre>
     39  *       List&lt;File&gt; list = ...
     40  *       Collections.sort(list, ExtensionFileComparator.EXTENSION_COMPARATOR);
     41  * </pre>
     42  * <p>
     43  * Example of a <i>reverse case-insensitive</i> file extension sort using the
     44  * {@link #EXTENSION_INSENSITIVE_REVERSE} singleton instance:
     45  * <pre>
     46  *       File[] array = ...
     47  *       Arrays.sort(array, ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE);
     48  * </pre>
     49  * <p>
     50  *
     51  * @version $Revision: 609243 $ $Date: 2008-01-06 00:30:42 +0000 (Sun, 06 Jan 2008) $
     52  * @since Commons IO 1.4
     53  */
     54 public class ExtensionFileComparator implements Comparator<File>, Serializable {
     55 
     56     /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
     57     public static final Comparator<File> EXTENSION_COMPARATOR = new ExtensionFileComparator();
     58 
     59     /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
     60     public static final Comparator<File> EXTENSION_REVERSE = new ReverseComparator<File>(EXTENSION_COMPARATOR);
     61 
     62     /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
     63     public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR = new ExtensionFileComparator(IOCase.INSENSITIVE);
     64 
     65     /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
     66     public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE
     67                                                 = new ReverseComparator<File>(EXTENSION_INSENSITIVE_COMPARATOR);
     68 
     69     /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
     70     public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
     71 
     72     /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
     73     public static final Comparator<File> EXTENSION_SYSTEM_REVERSE = new ReverseComparator<File>(EXTENSION_SYSTEM_COMPARATOR);
     74 
     75     /** Whether the comparison is case sensitive. */
     76     private final IOCase caseSensitivity;
     77 
     78     /**
     79      * Construct a case sensitive file extension comparator instance.
     80      */
     81     public ExtensionFileComparator() {
     82         this.caseSensitivity = IOCase.SENSITIVE;
     83     }
     84 
     85     /**
     86      * Construct a file extension comparator instance with the specified case-sensitivity.
     87      *
     88      * @param caseSensitivity how to handle case sensitivity, null means case-sensitive
     89      */
     90     public ExtensionFileComparator(IOCase caseSensitivity) {
     91         this.caseSensitivity = caseSensitivity == null ? IOCase.SENSITIVE : caseSensitivity;
     92     }
     93 
     94     /**
     95      * Compare the extensions of two files the specified case sensitivity.
     96      *
     97      * @param obj1 The first file to compare
     98      * @param obj2 The second file to compare
     99      * @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(File file1, File file2) {
    106         String suffix1 = FilenameUtils.getExtension(file1.getName());
    107         String suffix2 = FilenameUtils.getExtension(file2.getName());
    108         return caseSensitivity.checkCompareTo(suffix1, suffix2);
    109     }
    110 }
    111