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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package org.apache.commons.compress.utils;

import java.io.File;

/**
 * Generic file name utilities.
 * @since 1.20
 */
public class FileNameUtils {

    /**
     * Returns the extension (i.e. the part after the last ".") of a file.
     *
     * Will return an empty string if the file name doesn't contain
     * any dots. Only the last segment of a the file name is consulted
     * - i.e. all leading directories of the {@code filename}
     * parameter are skipped.
     *
     * @return the extension of filename
     * @param filename the name of the file to obtain the extension of.
     */
    public static String getExtension(final String filename) {
        if (filename == null) {
            return null;
        }

        final String name = new File(filename).getName();
        final int extensionPosition = name.lastIndexOf('.');
        if (extensionPosition < 0) {
            return "";
        }
        return name.substring(extensionPosition + 1);
    }

    /**
     * Returns the basename (i.e. the part up to and not including the
     * last ".") of the last path segment of a filename.
     *
     * Will return the file name itself if it doesn't contain any
     * dots. All leading directories of the {@code filename} parameter
     * are skipped.
     *
     * @return the basename of filename
     * @param filename the name of the file to obtain the basename of.
     */
    public static String getBaseName(final String filename) {
        if (filename == null) {
            return null;
        }

        final String name = new File(filename).getName();

        final int extensionPosition = name.lastIndexOf('.');
        if (extensionPosition < 0) {
            return name;
        }

        return name.substring(0, extensionPosition);
    }
}