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.Serializable;
021import java.nio.file.FileVisitResult;
022import java.nio.file.Files;
023import java.nio.file.Path;
024import java.nio.file.attribute.BasicFileAttributes;
025
026/**
027 * This filter accepts {@link File}s that are symbolic links.
028 * <p>
029 * For example, here is how to print out a list of the real files
030 * within the current directory:
031 * </p>
032 * <h2>Using Classic IO</h2>
033 * <pre>
034 * File dir = FileUtils.current();
035 * String[] files = dir.list(SymbolicLinkFileFilter.INSTANCE);
036 * for (String file : files) {
037 *     System.out.println(file);
038 * }
039 * </pre>
040 *
041 * <h2>Using NIO</h2>
042 * <pre>
043 * final Path dir = PathUtils.current();
044 * final AccumulatorPathVisitor visitor = AccumulatorPathVisitor.withLongCounters(SymbolicLinkFileFilter.INSTANCE);
045 * //
046 * // Walk one directory
047 * Files.<strong>walkFileTree</strong>(dir, Collections.emptySet(), 1, visitor);
048 * System.out.println(visitor.getPathCounters());
049 * System.out.println(visitor.getFileList());
050 * //
051 * visitor.getPathCounters().reset();
052 * //
053 * // Walk directory tree
054 * Files.<strong>walkFileTree</strong>(dir, visitor);
055 * System.out.println(visitor.getPathCounters());
056 * System.out.println(visitor.getDirList());
057 * System.out.println(visitor.getFileList());
058 * </pre>
059 * <h2>Deprecating Serialization</h2>
060 * <p>
061 * <em>Serialization is deprecated and will be removed in 3.0.</em>
062 * </p>
063 *
064 * @since 2.11.0
065 * @see FileFilterUtils#fileFileFilter()
066 */
067public class SymbolicLinkFileFilter extends AbstractFileFilter implements Serializable {
068    /*
069     * Note to developers: The unit test needs to create symbolic links to files. However, on
070     * Windows, this can't be done without admin privileges. This class is designed to allow a
071     * unit test to works around this by doing two things: 1) This separates the class logic from
072     * the call to identify a symbolic link, and 2) It allows the unit test to override that
073     * symbolic link call on Windows only.
074     * This means we can write unit tests that will run on all machines. On Windows, the unit test
075     * can't create a symbolic link without admin privileges, so the unit tests won't
076     * completely test all the necessary behavior on Windows, but they will still test the class
077     * logic. Be careful not to break this, but be aware of it when writing unit tests. You can
078     * still maintain this class and its unit tests on Windows. The one method that won't get
079     * tested on Windows is not likely to change, and will be tested properly when it gets run
080     * on Apache servers.
081     */
082
083    /**
084     * Singleton instance of file filter.
085     */
086    public static final SymbolicLinkFileFilter INSTANCE = new SymbolicLinkFileFilter();
087
088    private static final long serialVersionUID = 1L;
089
090    /**
091     * Restrictive constructor.
092     */
093    protected SymbolicLinkFileFilter() {
094    }
095
096    /**
097     * Constructs a new instance.
098     *
099     * @param onAccept What to do on acceptance.
100     * @param onReject What to do on rejection.
101     * @since 2.12.0.
102     */
103    public SymbolicLinkFileFilter(final FileVisitResult onAccept, final FileVisitResult onReject) {
104        super(onAccept, onReject);
105    }
106
107    /**
108     * Checks to see if the file is a symbolic link.
109     *
110     * @param file  the File to check
111     * @return true if the file exists and is a symbolic link to either another file or a directory,
112     *         false otherwise.
113     */
114    @Override
115    public boolean accept(final File file) {
116        return isSymbolicLink(file.toPath());
117    }
118
119    /**
120     * Checks to see if the file is a symbolic link.
121     *
122     * @param path the File Path to check
123     * @param attributes the path's basic attributes (may be null).
124     * @return {@code onAccept} from {@link #SymbolicLinkFileFilter(FileVisitResult, FileVisitResult)} if the file exists and is a symbolic link to either
125     *         another file or a directory; returns {@code onReject} otherwise.
126     */
127    @Override
128    public FileVisitResult accept(final Path path, final BasicFileAttributes attributes) {
129        return toFileVisitResult(isSymbolicLink(path));
130    }
131
132    /**
133     * Delegates to {@link Files#isSymbolicLink(Path)} for testing.
134     * <p>
135     * Using package access for unit tests. To facilitate unit testing, all calls to test if the file is a symbolic should go through this method. (See the unit
136     * test for why.)
137     * </p>
138     *
139     * @param filePath The filePath to test
140     * @return true if the file exists and is a symbolic link to either a file or directory, false otherwise.
141     */
142    boolean isSymbolicLink(final Path filePath) {
143        return Files.isSymbolicLink(filePath);
144    }
145}