/*
* 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 DirectoryStream extends Iterable, it is not a general-purpose Iterable as it supports only a single
Iterator; invoking the iterator method to obtain a second or subsequent iterator throws IllegalStateException.
An important property of the directory stream's Iterator is that its hasNext method is guaranteed to read-ahead by at least one element. If hasNext method returns true, and is followed by a call to the next method, it is guaranteed that the next method will not throw an exception due to an I/O error, or because the stream has been closed. The Iterator does not support the remove operation.
A DirectoryStream is opened upon creation and is closed by invoking the 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 Iterator, behaves as if the end of stream has been reached. Due to read-ahead, the 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 hasNext method returns false, and subsequent calls to the next method will throw 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 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 Iterator's hasNext or next methods to throw DirectoryIteratorException with the IOException as the cause. As stated above, the hasNext method is guaranteed to read-ahead by at least one element. This means that if hasNext method returns true, and is followed by a call to the next method, then it is guaranteed that the next method will not fail with a 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 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;
}
Type parameters: - <T> – The type of element returned by the iterator
See Also: Since: 1.7
/**
* 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.
*
* <p> <b> 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}. </b>
*
* <p> 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.
*
* <p> 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:
* <pre>
* Path dir = ...
* try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
* for (Path entry: stream) {
* ...
* }
* }
* </pre>
*
* <p> 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}.
*
* <p> A directory stream is not required to be <i>asynchronously closeable</i>.
* 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.
*
* <p> 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}.
*
* <p> 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.
*
* <p> The iterator is <i>weakly consistent</i>. 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.
*
* <p> <b>Usage Examples:</b>
* Suppose we want a list of the source files in a directory. This example uses
* both the for-each and try-with-resources constructs.
* <pre>
* 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;
* }
* </pre>
* @param <T> The type of element returned by the iterator
*
* @since 1.7
*
* @see Files#newDirectoryStream(Path)
*/
public interface DirectoryStream<T>
extends Closeable, Iterable<T> {
An interface that is implemented by objects that decide if a directory entry should be accepted or filtered. A Filter is passed as the parameter to the Files.newDirectoryStream(Path, Filter<? super Path>) method when opening a directory to iterate over the entries in the directory. Type parameters: - <T> – the type of the directory entry
Since: 1.7
/**
* 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 <T> the type of the directory entry
*
* @since 1.7
*/
@FunctionalInterface
public static interface Filter<T> {
Decides if the given directory entry should be accepted or filtered.
Params: - entry –
the directory entry to be tested
Throws: - IOException –
If an I/O error occurs
Returns: true if the directory entry should be accepted
/**
* 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 DirectoryStream. Throws: - IllegalStateException –
if this directory stream is closed or the iterator has already
been returned
Returns: the iterator associated with this DirectoryStream
/**
* 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<T> iterator();
}