jdk.nio.file.DirectoryStream
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; }
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;
}iteratorclj
(iterator this)Returns the iterator associated with this DirectoryStream.
returns: the iterator associated with this DirectoryStream - java.util.Iterator<T>
throws: java.lang.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 DirectoryStream - `java.util.Iterator<T>` throws: java.lang.IllegalStateException - if this directory stream is closed or the iterator has already been returned
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