Interface DirectoryStream<T>
- 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 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; }
- Since:
- 1.7
- See Also:
Files.newDirectoryStream(Path)
Nested Class Summary
Modifier and Type | Interface | Description |
---|---|---|
static interface | DirectoryStream.Filter<T> | An interface that is implemented by objects that decide if a directory entry should be accepted or filtered. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
Iterator<T> | iterator() | Returns the iterator associated with this |
Methods declared in interface java.io.Closeable
close
Methods declared in interface java.lang.Iterable
forEach, spliterator
Method Detail
iterator
Iterator<T> iterator()
Returns the iterator associated with this DirectoryStream
.
- Specified by:
-
iterator
in interfaceIterable<T>
- Returns:
- the iterator associated with this
DirectoryStream
- Throws:
-
IllegalStateException
- if this directory stream is closed or the iterator has already been returned