    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 */
    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 <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 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 * 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 *       ((AbstractFileComparator) 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 *       ((AbstractFileComparator) ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE).sort(array);
    048 * </pre>
    049 * <p>
    050 *
    051 * @since 1.4
    052 */
    053public class ExtensionFileComparator extends AbstractFileComparator implements Serializable {
    054
    055    private static final long serialVersionUID = 1928235200184222815L;
    056
    057    /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    058    public static final Comparator<File> EXTENSION_COMPARATOR = new ExtensionFileComparator();
    059
    060    /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
    061    public static final Comparator<File> EXTENSION_REVERSE = new ReverseComparator(EXTENSION_COMPARATOR);
    062
    063    /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    064    public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR
    065                                                = new ExtensionFileComparator(IOCase.INSENSITIVE);
    066
    067    /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
    068    public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE
    069                                                = new ReverseComparator(EXTENSION_INSENSITIVE_COMPARATOR);
    070
    071    /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
    072    public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
    073
    074    /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
    075    public static final Comparator<File> EXTENSION_SYSTEM_REVERSE = new ReverseComparator(EXTENSION_SYSTEM_COMPARATOR);
    076
    077    /** Whether the comparison is case sensitive. */
    078    private final IOCase caseSensitivity;
    079
    080    /**
    081     * Construct a case sensitive file extension comparator instance.
    082     */
    083    public ExtensionFileComparator() {
    084        this.caseSensitivity = IOCase.SENSITIVE;
    085    }
    086
    087    /**
    088     * Construct a file extension comparator instance with the specified case-sensitivity.
    089     *
    090     * @param caseSensitivity how to handle case sensitivity, null means case-sensitive
    091     */
    092    public ExtensionFileComparator(final IOCase caseSensitivity) {
    093        this.caseSensitivity = caseSensitivity == null ? IOCase.SENSITIVE : caseSensitivity;
    094    }
    095
    096    /**
    097     * Compare the extensions of two files the specified case sensitivity.
    098     *
    099     * @param file1 The first file to compare
    100     * @param file2 The second file to compare
    101     * @return a negative value if the first file's extension
    102     * is less than the second, zero if the extensions are the
    103     * same and a positive value if the first files extension
    104     * is greater than the second file.
    105     *
    106     */
    107    @Override
    108    public int compare(final File file1, final File file2) {
    109        final String suffix1 = FilenameUtils.getExtension(file1.getName());
    110        final String suffix2 = FilenameUtils.getExtension(file2.getName());
    111        return caseSensitivity.checkCompareTo(suffix1, suffix2);
    112    }
    113
    114    /**
    115     * String representation of this file comparator.
    116     *
    117     * @return String representation of this file comparator
    118     */
    119    @Override
    120    public String toString() {
    121        return super.toString() + "[caseSensitivity=" + caseSensitivity + "]";
    122    }
    123}