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| 1 | /* | ||
| 2 | * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.nio.file; | ||
| 27 | |||
| 28 | import java.util.Iterator; | ||
| 29 | import java.io.Closeable; | ||
| 30 | import java.io.IOException; | ||
| 31 | |||
| 32 | /** | ||
| 33 | * An object to iterate over the entries in a directory. A directory stream | ||
| 34 | * allows for the convenient use of the for-each construct to iterate over a | ||
| 35 | * directory. | ||
| 36 | * | ||
| 37 | * <p> <b> While {@code DirectoryStream} extends {@code Iterable}, it is not a | ||
| 38 | * general-purpose {@code Iterable} as it supports only a single {@code | ||
| 39 | * Iterator}; invoking the {@link #iterator iterator} method to obtain a second | ||
| 40 | * or subsequent iterator throws {@code IllegalStateException}. </b> | ||
| 41 | * | ||
| 42 | * <p> An important property of the directory stream's {@code Iterator} is that | ||
| 43 | * its {@link Iterator#hasNext() hasNext} method is guaranteed to read-ahead by | ||
| 44 | * at least one element. If {@code hasNext} method returns {@code true}, and is | ||
| 45 | * followed by a call to the {@code next} method, it is guaranteed that the | ||
| 46 | * {@code next} method will not throw an exception due to an I/O error, or | ||
| 47 | * because the stream has been {@link #close closed}. The {@code Iterator} does | ||
| 48 | * not support the {@link Iterator#remove remove} operation. | ||
| 49 | * | ||
| 50 | * <p> A {@code DirectoryStream} is opened upon creation and is closed by | ||
| 51 | * invoking the {@code close} method. Closing a directory stream releases any | ||
| 52 | * resources associated with the stream. Failure to close the stream may result | ||
| 53 | * in a resource leak. The try-with-resources statement provides a useful | ||
| 54 | * construct to ensure that the stream is closed: | ||
| 55 | * <pre> | ||
| 56 | * Path dir = ... | ||
| 57 | * try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) { | ||
| 58 | * for (Path entry: stream) { | ||
| 59 | * ... | ||
| 60 | * } | ||
| 61 | * } | ||
| 62 | * </pre> | ||
| 63 | * | ||
| 64 | * <p> Once a directory stream is closed, then further access to the directory, | ||
| 65 | * using the {@code Iterator}, behaves as if the end of stream has been reached. | ||
| 66 | * Due to read-ahead, the {@code Iterator} may return one or more elements | ||
| 67 | * after the directory stream has been closed. Once these buffered elements | ||
| 68 | * have been read, then subsequent calls to the {@code hasNext} method returns | ||
| 69 | * {@code false}, and subsequent calls to the {@code next} method will throw | ||
| 70 | * {@code NoSuchElementException}. | ||
| 71 | * | ||
| 72 | * <p> A directory stream is not required to be <i>asynchronously closeable</i>. | ||
| 73 | * If a thread is blocked on the directory stream's iterator reading from the | ||
| 74 | * directory, and another thread invokes the {@code close} method, then the | ||
| 75 | * second thread may block until the read operation is complete. | ||
| 76 | * | ||
| 77 | * <p> If an I/O error is encountered when accessing the directory then it | ||
| 78 | * causes the {@code Iterator}'s {@code hasNext} or {@code next} methods to | ||
| 79 | * throw {@link DirectoryIteratorException} with the {@link IOException} as the | ||
| 80 | * cause. As stated above, the {@code hasNext} method is guaranteed to | ||
| 81 | * read-ahead by at least one element. This means that if {@code hasNext} method | ||
| 82 | * returns {@code true}, and is followed by a call to the {@code next} method, | ||
| 83 | * then it is guaranteed that the {@code next} method will not fail with a | ||
| 84 | * {@code DirectoryIteratorException}. | ||
| 85 | * | ||
| 86 | * <p> The elements returned by the iterator are in no specific order. Some file | ||
| 87 | * systems maintain special links to the directory itself and the directory's | ||
| 88 | * parent directory. Entries representing these links are not returned by the | ||
| 89 | * iterator. | ||
| 90 | * | ||
| 91 | * <p> The iterator is <i>weakly consistent</i>. It is thread safe but does not | ||
| 92 | * freeze the directory while iterating, so it may (or may not) reflect updates | ||
| 93 | * to the directory that occur after the {@code DirectoryStream} is created. | ||
| 94 | * | ||
| 95 | * <p> <b>Usage Examples:</b> | ||
| 96 | * Suppose we want a list of the source files in a directory. This example uses | ||
| 97 | * both the for-each and try-with-resources constructs. | ||
| 98 | * <pre> | ||
| 99 | * List<Path> listSourceFiles(Path dir) throws IOException { | ||
| 100 | * List<Path> result = new ArrayList<>(); | ||
| 101 | * try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.{c,h,cpp,hpp,java}")) { | ||
| 102 | * for (Path entry: stream) { | ||
| 103 | * result.add(entry); | ||
| 104 | * } | ||
| 105 | * } catch (DirectoryIteratorException ex) { | ||
| 106 | * // I/O error encounted during the iteration, the cause is an IOException | ||
| 107 | * throw ex.getCause(); | ||
| 108 | * } | ||
| 109 | * return result; | ||
| 110 | * } | ||
| 111 | * </pre> | ||
| 112 | * @param <T> The type of element returned by the iterator | ||
| 113 | * | ||
| 114 | * @since 1.7 | ||
| 115 | * | ||
| 116 | * @see Files#newDirectoryStream(Path) | ||
| 117 | */ | ||
| 118 | |||
| 119 | public interface DirectoryStream<T> | ||
| 120 | extends Closeable, Iterable<T> | ||
| 121 | { | ||
| 122 | /** | ||
| 123 | * An interface that is implemented by objects that decide if a directory | ||
| 124 | * entry should be accepted or filtered. A {@code Filter} is passed as the | ||
| 125 | * parameter to the {@link Files#newDirectoryStream(Path,DirectoryStream.Filter)} | ||
| 126 | * method when opening a directory to iterate over the entries in the | ||
| 127 | * directory. | ||
| 128 | * | ||
| 129 | * @param <T> the type of the directory entry | ||
| 130 | * | ||
| 131 | * @since 1.7 | ||
| 132 | */ | ||
| 133 | public static interface Filter<T> { | ||
| 134 | /** | ||
| 135 | * Decides if the given directory entry should be accepted or filtered. | ||
| 136 | * | ||
| 137 | * @param entry | ||
| 138 | * the directory entry to be tested | ||
| 139 | * | ||
| 140 | * @return {@code true} if the directory entry should be accepted | ||
| 141 | * | ||
| 142 | * @throws IOException | ||
| 143 | * If an I/O error occurs | ||
| 144 | */ | ||
| 145 | boolean accept(T entry) throws IOException; | ||
| 146 | } | ||
| 147 | |||
| 148 | /** | ||
| 149 | * Returns the iterator associated with this {@code DirectoryStream}. | ||
| 150 | * | ||
| 151 | * @return the iterator associated with this {@code DirectoryStream} | ||
| 152 | * | ||
| 153 | * @throws IllegalStateException | ||
| 154 | * if this directory stream is closed or the iterator has already | ||
| 155 | * been returned | ||
| 156 | */ | ||
| 157 | @Override | ||
| 158 | Iterator<T> iterator(); | ||
| 159 | } | ||