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- Type Parameters:
T- The type of element returned by the iterator
- All Superinterfaces:
AutoCloseable,Closeable,Iterable<T>
- All Known Subinterfaces:
SecureDirectoryStream<T>
public interface DirectoryStream<T> extends Closeable, Iterable<T>
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
DirectoryStreamextendsIterable, it is not a general-purposeIterableas it supports only a singleIterator; invoking theiteratormethod to obtain a second or subsequent iterator throwsIllegalStateException.An important property of the directory stream's
Iteratoris that itshasNextmethod is guaranteed to read-ahead by at least one element. IfhasNextmethod returnstrue, and is followed by a call to thenextmethod, it is guaranteed that thenextmethod will not throw an exception due to an I/O error, or because the stream has beenclosed. TheIteratordoes not support theremoveoperation.A
DirectoryStreamis opened upon creation and is closed by invoking theclosemethod. 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, theIteratormay return one or more elements after the directory stream has been closed. Once these buffered elements have been read, then subsequent calls to thehasNextmethod returnsfalse, and subsequent calls to thenextmethod will throwNoSuchElementException.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
closemethod, 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'shasNextornextmethods to throwDirectoryIteratorExceptionwith theIOExceptionas the cause. As stated above, thehasNextmethod is guaranteed to read-ahead by at least one element. This means that ifhasNextmethod returnstrue, and is followed by a call to thenextmethod, then it is guaranteed that thenextmethod will not fail with aDirectoryIteratorException.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
DirectoryStreamis 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; }- Since:
- 1.7
- See Also:
Files.newDirectoryStream(Path)
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Nested Class Summary
Nested Classes Modifier and Type Interface Description static interfaceDirectoryStream.Filter<T>An interface that is implemented by objects that decide if a directory entry should be accepted or filtered.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description Iterator<T>iterator()Returns the iterator associated with thisDirectoryStream.-
Methods declared in interface java.lang.Iterable
forEach, spliterator
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Method Detail
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iterator
Iterator<T> iterator()
Returns the iterator associated with thisDirectoryStream.- Specified by:
iteratorin interfaceIterable<T>- Returns:
- the iterator associated with this
DirectoryStream - Throws:
IllegalStateException- if this directory stream is closed or the iterator has already been returned
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