/* * Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.nio.file; import java.util.Iterator; import java.io.Closeable; import java.io.IOException; /** * An object to iterate over the entries in a directory. A directory stream * allows for the convenient use of the for-each construct to iterate over a * directory. * *

While {@code DirectoryStream} extends {@code Iterable}, it is not a * general-purpose {@code Iterable} as it supports only a single {@code * Iterator}; invoking the {@link #iterator iterator} method to obtain a second * or subsequent iterator throws {@code IllegalStateException}. * *

An important property of the directory stream's {@code Iterator} is that * its {@link Iterator#hasNext() hasNext} method is guaranteed to read-ahead by * at least one element. If {@code hasNext} method returns {@code true}, and is * followed by a call to the {@code next} method, it is guaranteed that the * {@code next} method will not throw an exception due to an I/O error, or * because the stream has been {@link #close closed}. The {@code Iterator} does * not support the {@link Iterator#remove remove} operation. * *

A {@code DirectoryStream} is opened upon creation and is closed by * invoking the {@code close} method. Closing a directory stream releases any * resources associated with the stream. Failure to close the stream may result * in a resource leak. The try-with-resources statement provides a useful * construct to ensure that the stream is closed: *

 *   Path dir = ...
 *   try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
 *       for (Path entry: stream) {
 *           ...
 *       }
 *   }
 * 
* *

Once a directory stream is closed, then further access to the directory, * using the {@code Iterator}, behaves as if the end of stream has been reached. * Due to read-ahead, the {@code Iterator} may return one or more elements * after the directory stream has been closed. Once these buffered elements * have been read, then subsequent calls to the {@code hasNext} method returns * {@code false}, and subsequent calls to the {@code next} method will throw * {@code NoSuchElementException}. * *

A directory stream is not required to be asynchronously closeable. * If a thread is blocked on the directory stream's iterator reading from the * directory, and another thread invokes the {@code close} method, then the * second thread may block until the read operation is complete. * *

If an I/O error is encountered when accessing the directory then it * causes the {@code Iterator}'s {@code hasNext} or {@code next} methods to * throw {@link DirectoryIteratorException} with the {@link IOException} as the * cause. As stated above, the {@code hasNext} method is guaranteed to * read-ahead by at least one element. This means that if {@code hasNext} method * returns {@code true}, and is followed by a call to the {@code next} method, * then it is guaranteed that the {@code next} method will not fail with a * {@code DirectoryIteratorException}. * *

The elements returned by the iterator are in no specific order. Some file * systems maintain special links to the directory itself and the directory's * parent directory. Entries representing these links are not returned by the * iterator. * *

The iterator is weakly consistent. It is thread safe but does not * freeze the directory while iterating, so it may (or may not) reflect updates * to the directory that occur after the {@code DirectoryStream} is created. * *

Usage Examples: * Suppose we want a list of the source files in a directory. This example uses * both the for-each and try-with-resources constructs. *

 *   List<Path> listSourceFiles(Path dir) throws IOException {
 *       List<Path> result = new ArrayList<>();
 *       try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.{c,h,cpp,hpp,java}")) {
 *           for (Path entry: stream) {
 *               result.add(entry);
 *           }
 *       } catch (DirectoryIteratorException ex) {
 *           // I/O error encounted during the iteration, the cause is an IOException
 *           throw ex.getCause();
 *       }
 *       return result;
 *   }
 * 
* @param The type of element returned by the iterator * * @since 1.7 * * @see Files#newDirectoryStream(Path) */ public interface DirectoryStream extends Closeable, Iterable { /** * An interface that is implemented by objects that decide if a directory * entry should be accepted or filtered. A {@code Filter} is passed as the * parameter to the {@link Files#newDirectoryStream(Path,DirectoryStream.Filter)} * method when opening a directory to iterate over the entries in the * directory. * * @param the type of the directory entry * * @since 1.7 */ @FunctionalInterface public static interface Filter { /** * Decides if the given directory entry should be accepted or filtered. * * @param entry * the directory entry to be tested * * @return {@code true} if the directory entry should be accepted * * @throws IOException * If an I/O error occurs */ boolean accept(T entry) throws IOException; } /** * Returns the iterator associated with this {@code DirectoryStream}. * * @return the iterator associated with this {@code DirectoryStream} * * @throws IllegalStateException * if this directory stream is closed or the iterator has already * been returned */ @Override Iterator iterator(); }