This document provides an overview of new features in NIO 2 and asynchronous I/O in Java. It discusses buffers, channels, selectors, file system APIs, file change notification, and asynchronous operations using futures and completion handlers. The key aspects covered include non-blocking I/O, readiness selection, file locking, memory mapping, and file attributes.

1. What's New in NIO 2 Ranjith Kumar N JUG-Chennai 9th June 2011

3. Channels

5. New File System API

7. NIO Features Channel and Buffers File locking Memory Mapped Files Scatter and Gather Channel to Channel Transfer Non-Blocking Sockets Multiplexed I/O

8. Buffersjava.nio

9. Buffer's Basic Attributes: Capacity Limit Position Mark

10. Buffer Basic Operations: Creating Filling and Draining Flipping and Rewind Marking Comparing Duplicating

11. Creating public static XXXBuffer allocate (int capacity) public static XXXBuffer wrap (XXX [] array) public static XXXBuffer wrap (XXX [] array, int offset,int length) For e.g. CharBuffer charBuffer= CharBuffer.allocate(10); char [] charArray = new char [10]; CharBuffercharbuffer = CharBuffer.wrap (charArray ); CharBuffercharbuffer = CharBuffer.wrap (charArray, 2, 7);

12. Filling and Draining XXXBuffer put (XXX b); XXXBuffer put (int index, XXX b); XXX get( ); XXX get(int index); XXXBufferput (XXX[] src); XXXBuffer put(XXX [] src, int offset, int length); XXXBuffer get(XXX[] dest); XXXBuffer get(XXX [] dest, int offset, int length);

13. Flipping and Rewind Manually Flipping a Buffer: buffer.limit(buffer.position( )).position(0) API provides Flip and rewind method: Buffer flip() Buffer rewind()

14. Marking Buffer mark() Buffer reset() For e.g buffer.position(2).mark( ).position(4);

15. Marking - cont. After calling reset method

17. Both buffers have the same number of remaining elements.

19. Comparing – cont. Two buffers considered to be unequal

20. Duplicating CharBuffer duplicate( ); CharBuffer asReadOnlyBuffer( ); CharBuffer slice( ); For e.g CharBuffer buffer = CharBuffer.allocate (8); buffer.position(3).limit (6).mark( ).position (5); CharBuffer dupeBuffer = buffer.duplicate( ); buffer.clear( );

21. Duplicating – cont.

22. Duplicating – cont. e.g. CharBuffer buffer = CharBuffer.allocate (8); buffer.position(3).limit (5); CharBuffer sliceBuffer = buffer.slice( );

23. Byte Buffers

25. Copy the content of the nondirect buffer to the temporary buffer.

26. Perform the low-level I/O operation using the temporary buffer.

28. View Buffers: cont. ByteBuffer byteBuffer =ByteBuffer.allocate (7); CharBuffer charBuffer = byteBuffer.asCharBuffer( );

29. Channeljava.nio.channels

30. Channel basics Creating Reading/Writing Scatter/Gather Closing

31. Creating SocketChannel sc = SocketChannel.open( ); ServerSocketChannelssc = ServerSocketChannel.open( ); DatagramChannel dc = DatagramChannel.open( ); RandomAccessFileraf = new RandomAccessFile ("somefile", "r"); FileChannel fc = raf.getChannel( );

33. Scatter/Gather ScatteringByteChannel read (ByteBuffer [] dsts) read (ByteBuffer [] dsts, int offset, int length) GatheringByteChannel write(ByteBuffer[] srcs) write(ByteBuffer[] srcs, int offset, int length)

36. File Locking FileLock lock( ) FileLock lock (long position, long size,boolean shared) FileLocktryLock( ) FileLocktryLock (long position, long size,boolean shared)

37. Memory-Mapped Files MappedByteBuffer map (MapMode mode, long position,long size)

38. Channel 2 Channel transfer transferTo (long position, long count, WritableByteChannel target) transferFrom (ReadableByteChannel src,long position, long count)

39. Socket Channelsjava.nio.channels

40. Non-blocking Mode SelectableChannel configureBlocking (boolean block) boolean isBlocking( ) Object blockingLock( ) e.g. SocketChannel sc = SocketChannel.open( ); sc.configureBlocking (false); // nonblocking mode sc.configureBlocking (true); // blocking mode

41. Readiness Selection Socket channels can be check for readiness A single thread can monitor a large number of socket Steps to do readiness selection Create a Selector instance Register one or more non-blocking channels with it Implement a infinite loop and wait for events Get the selected keys list and iterate the keys Process the events. Remove the key from the list

42. Readiness Selection Selector selector = Selector.open(); ServerSocketChannelserverChannel = ServerSocketChannel.open(); serverChannel.socket().bind (new InetSocketAddress (port)); serverChannel.configureBlocking (false); SelectionKeyregisteredkey = serverChannel.register (selector, SelectionKey.OP_ACCEPT); while (true) { selector.select(); Iterator it = selector.selectedKeys().iterator(); while (it.hasNext()) { SelectionKey key = (SelectionKey) it.next(); //process it.remove(); } }

43. Selector Key Methods: Selector open( ) int select( ) int select (long timeout) int selectNow( ) Set keys( ) Set selectedKeys( )

44. SelectableChannel Key methods: SelectionKey register (Selector sel, int ops) booleanisRegistered( ); SelectionKeykeyFor (Selector sel); int validOps( );

45. SelectionKey Key methods: SelectableChannel channel( ) Selector selector( ) void cancel( ) boolean isValid( ) booleanisReadable( ) boolean isWritable( ) boolean isConnectable( ) boolean isAcceptable( ) Operations to select: int OP_READ int OP_WRITE int OP_CONNECT int OP_ACCEPT

46. NIO 2JSR-203

47. FileChanneljava.nio.channels FileChannel open(Path path, Set<? extends OpenOption> options, FileAttribute<?>... attrs) FileChannel open(Path path, OpenOption... options) e.g. Path file= Paths.get("C:homejugcread.txt"); FileChannelfc = (FileChannel.open(file, WRITE, APPEND ));

48. StandardOpenOption Enumjava.nio.file

49. SeekableByteChannel A byte channel that maintains a current position and allows the position to be changed. Key Methods SeekableByteChannel position(long newPosition) SeekableByteChannel truncate(long size)

50. NetworkChannel & MulticastChanneljava.nio.channels NetworkChannels: All the network-oriented channels implements the new NetworkChannel interface We can easily bind the channel socket, set and query for socket options MulticastChannels: We can send and receive IP datagrams from a complete group Implement by DatagramChannel and AsynchronousDatagramChannel

51. Pathjava.nio.file Locates a file using a system dependent path Defines methods to access and manipulate paths Defines methods to access files

52. Creating a Path // Microsoft Windows Path p1 = Paths.get("C:homejoefoo"); // Solaris syntax Path path = Paths.get("/home/joe/foo"); Path p4 = FileSystems.getDefault().getPath("/users/sally");

53. Key Methods Path normalize() Path toAbsolutePath() Path toRealPath(LinkOption... options) Path resolve(Path other) Path relativize(Path other) Pathjava.nio.file

54. Files java.nio.file Helper Class Copy Move Delete Create file, directory and links

55. Copy long copy(InputStream in, Path target, CopyOption... options) long copy(Path source, OutputStream out) Path copy(Path source, Path target, CopyOption... options)

56. Move & Delete void delete(Path path) booleandeleteIfExists(Path path) Path move(Path source, Path target, CopyOption... options)

57. File, Directory and link Path createFile(Path path, FileAttribute<?>... attrs) Path createTempFile(String prefix, String suffix, FileAttribute<?>... attrs) Path createDirectory(Path dir, FileAttribute<?>... attrs) Path createDirectories(Path dir, FileAttribute<?>... attrs) Path createTempDirectory(Path dir, String prefix, FileAttribute<?>... attrs) Path createSymbolicLink(Path link, Path target, FileAttribute<?>... attrs)

58. Walk File Tree Walk a file tree rooted at a given starting file Implement FileVisitor interface Initiate the process by calling anyone of the below method of java.nio.file.FilesClass walkFileTree(Path start, FileVisitor<? super Path> visitor) walkFileTree(Path start, Set<FileVisitOption> options, intmaxDepth, FileVisitor<? super Path> visitor)

59. FileVisitorjava.nio.file FileVisitResultpreVisitDirectory(T dir); FileVisitResultvisitFile(T file, BasicFileAttributes attrs); FileVisitResultpostVisitDirectory(T dir, IOExceptionexc); FileVisitResultpreVisitDirectoryFailed(T dir, IOExceptionexc); FileVisitResultvisitFileFailed(T file, IOExceptionexc);

60. FileVisitor Callback Methods Start Previsit Directory postVisitDirectory File 1 Link Root 1 visitFile visitFile Previsit Directory postVisitDirectory File 2 File 3 visitFile visitFile

61. File Change Notification Looking for file changes in FileSystem Using the native event facility whenever available Steps required to implement a watch service Create a WatchService "watcher" for the file system. For each directory that you want monitored, register it with the watcher. Implement an infinite loop to wait for incoming events Retrieve the key from the watcher's queue. Process all the events associated with the Key. Reset the key, and resume waiting for events. Close the service

62. File Change Notification – cont. WatchService watcher = FileSystems.getDefault().newWatchService(); Path dir= Paths.get("C:homewatchdir"); WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY); for( ; ; ){ WatchKeysignalledkey = watcher.take(); for (WatchEvent<?> event: signalledkey .pollEvents()) { WatchEvent.Kind<?> kind = event.kind(); // process the event } boolean valid = signalledkey .reset(); if (!valid) { break; } }

63. WatchServicejava.nio.file Watch registered objects for events and changes Key Methods WatchKey poll() WatchKey poll(long timeout, TimeUnit unit) WatchKey take() void close()

64. WatchKeyjava.nio.file WatchKey represents registration of a watchable object with a WatchService. Key Methods: List<WatchEvent<?>> pollEvents() Watchable watchable() boolean reset() boolean isValid() void cancel()

65. File Attributesjava.nio.file.attribute Meta-data associated with file Generalized metadata API Fetch a file's attributes in one bulk operation Map<String,Object> readAttributes(Path, String, LinkOption...) <A extends BasicFileAttributes> readAttributes(Path, Class<A>, LinkOption...) Grouping of related attributes and Views to access the attribute groups.

66. Attributes View BasicFileAttributeView DosFileAttributeView PosixFileAttributeView FileOwnerAttributeView UserDefinedFileAttributeView File Attributesjava.nio.file.attribute

67. File Attributesjava.nio.file.attribute Path file = Paths.get("C:homefile.txt"); ; BasicFileAttributesattr = Files.readAttributes(file, BasicFileAttributes.class); DosFileAttributesdosattr = Files.readAttributes(file, DosFileAttributes.class); PosixFileAttributesposixattr = Files.readAttributes(file, PosixFileAttributes.class);

68. Asynchronous I/Ojava.nio.channels They provide asynchronous operations for both sockets and files. All operations work in non-blocking mode. All the asynchronous I/O operations have one of two forms : The first one returns a java.util.concurrent.Future that represent the pending result The second one is created using a CompletionHandler.

69. Futurejava.util.concurrent AsynchronousFileChannel channel = AsynchronousFileChannel.open(Paths.get(“C:homeasyncfile.txt ")); ByteBuffer buffer = ByteBuffer.allocate(100); Future result = channel.read(buffer, 100); boolean done = result.isDone();

70. CompletionHandler Future result = channel.read(buffer, 100, buffer, new CompletionHandler(){ public void completed(Integer result, ByteBuffer buffer){ //Compute the result } public void failed(Throwable exception, ByteBuffer buffer){ // Handle the error } });

71. References: Java NIO by Ron Hitchens Publisher: O’Reilly http://java.sun.com/developer/technicalArticles/javase/nio/ http://download.oracle.com/javase/tutorial/essential/io/index.html

72. Thanks U!!!!