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 */
17package org.apache.commons.io.comparator;
18
19import java.io.File;
20import java.io.Serializable;
21import java.util.Comparator;
22
23import org.apache.commons.io.FilenameUtils;
24import 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 */
54public 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