    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.filefilter;
    018
    019import java.io.File;
    020import java.io.IOException;
    021import java.io.Serializable;
    022import java.nio.file.FileVisitResult;
    023import java.nio.file.Files;
    024import java.nio.file.Path;
    025import java.nio.file.attribute.BasicFileAttributes;
    026import java.util.stream.Stream;
    027
    028import org.apache.commons.io.IOUtils;
    029
    030/**
    031 * This filter accepts files or directories that are empty.
    032 * <p>
    033 * If the {@code File} is a directory it checks that it contains no files.
    034 * </p>
    035 * <p>
    036 * Example, showing how to print out a list of the current directory's empty files/directories:
    037 * </p>
    038 * <h2>Using Classic IO</h2>
    039 * <pre>
    040 * File dir = new File(".");
    041 * String[] files = dir.list(EmptyFileFilter.EMPTY);
    042 * for (String file : files) {
    043 *     System.out.println(file);
    044 * }
    045 * </pre>
    046 *
    047 * <p>
    048 * Example, showing how to print out a list of the current directory's non-empty files/directories:
    049 * </p>
    050 *
    051 * <pre>
    052 * File dir = new File(".");
    053 * String[] files = dir.list(EmptyFileFilter.NOT_EMPTY);
    054 * for (String file : files) {
    055 *     System.out.println(file);
    056 * }
    057 * </pre>
    058 *
    059 * <h2>Using NIO</h2>
    060 * <pre>
    061 * final Path dir = Paths.get("");
    062 * final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(EmptyFileFilter.EMPTY);
    063 * //
    064 * // Walk one dir
    065 * Files.<b>walkFileTree</b>(dir, Collections.emptySet(), 1, visitor);
    066 * System.out.println(visitor.getPathCounters());
    067 * System.out.println(visitor.getFileList());
    068 * //
    069 * visitor.getPathCounters().reset();
    070 * //
    071 * // Walk dir tree
    072 * Files.<b>walkFileTree</b>(dir, visitor);
    073 * System.out.println(visitor.getPathCounters());
    074 * System.out.println(visitor.getDirList());
    075 * System.out.println(visitor.getFileList());
    076 * </pre>
    077 *
    078 * @since 1.3
    079 */
    080public class EmptyFileFilter extends AbstractFileFilter implements Serializable {
    081
    082    /** Singleton instance of <i>empty</i> filter */
    083    public static final IOFileFilter EMPTY = new EmptyFileFilter();
    084
    085    /** Singleton instance of <i>not-empty</i> filter */
    086    public static final IOFileFilter NOT_EMPTY = EMPTY.negate();
    087
    088    private static final long serialVersionUID = 3631422087512832211L;
    089
    090    /**
    091     * Restrictive constructor.
    092     */
    093    protected EmptyFileFilter() {
    094    }
    095
    096    /**
    097     * Checks to see if the file is empty.
    098     *
    099     * @param file the file or directory to check
    100     * @return {@code true} if the file or directory is <i>empty</i>, otherwise {@code false}.
    101     */
    102    @Override
    103    public boolean accept(final File file) {
    104        if (file.isDirectory()) {
    105            final File[] files = file.listFiles();
    106            return IOUtils.length(files) == 0;
    107        }
    108        return file.length() == 0;
    109    }
    110
    111    /**
    112     * Checks to see if the file is empty.
    113     * @param file the file or directory to check
    114     *
    115     * @return {@code true} if the file or directory is <i>empty</i>, otherwise {@code false}.
    116     * @since 2.9.0
    117     */
    118    @Override
    119    public FileVisitResult accept(final Path file, final BasicFileAttributes attributes) {
    120        try {
    121            if (Files.isDirectory(file)) {
    122                try (Stream<Path> stream = Files.list(file)) {
    123                    return toFileVisitResult(!stream.findFirst().isPresent(), file);
    124                }
    125            }
    126            return toFileVisitResult(Files.size(file) == 0, file);
    127        } catch (final IOException e) {
    128            return handle(e);
    129        }
    130    }
    131
    132}