Java NIO. Rein Raudjärv Nov 19th 2012 Java Fundamentals

Transcription

1 Java NIO Rein Raudjärv Nov 19th 2012 Java Fundamentals

2 Agenda 1. NIO 1. Basics 2. Channels 3. Selectors 2. NIO.2 (File I/O) 1. Basics 2. Metadata

3 NIO BASICS

4 Based On Jakob Jenkov hjp://tutorials.jenkov.com/java- nio/index.html

5 What is NIO? Java NIO (New IO) is an alternaqve IO API for Java Since Java 1.4 (2002) It enables you to do asynchronous IO.

6 Reading Example FileChannel fc = new RandomAccessFile("in.txt", "r").getchannel(); try { ByteBuffer buf = ByteBuffer.allocate(48); while (fc.read(buf)!= - 1) { buf.flip(); while (buf.hasremaining()) System.out.print((char) buf.get()); buf.clear(); } } finally { fc.close(); }

7 WriQng Example FileChannel fc = new RandomAccessFile("out.txt", "rw").getchannel(); try { String data = "Hello"; ByteBuffer buf = ByteBuffer.allocate(48); buf.clear(); buf.put(data.getbytes()); buf.flip(); fc.write(buf); } finally { fc.close(); }

8 WriQng Example (2) FileChannel fc = new RandomAccessFile( "out.txt", "rw ).getchannel(); try { } String data = "Hello"; ByteBuffer buf = ByteBuffer.wrap(data.getBytes()); fc.write(buf); finally { fc.close(); }

9 Channels FileChannel DatagramChannel SocketChannel ServerSocketChannel

10 Buffers ByteBuffer CharBuffer DoubleBuffer FloatBuffer IntBuffer LongBuffer ShortBuffer

11 Buffer State Mode (WriQng or Reading) Capacity PosiQon Limit 0 <= posiqon <= limit <= capacity

12 Buffer State

13 Buffer Usage 1. Write data into the Buffer 2. Call buffer.flip() 3. Read data out of the Buffer 4. Call buffer.clear() or buffer.compact()

14 WriQng Data to a Buffer Copy data from a Channel into a Buffer int bytesread = inchannel.read(buf); Write data into the Buffer yourself, via the buffer's put() methods. buf.put(127);

15 Reading Data from a Buffer Copy data from a buffer into a Channel. int byteswrijen = outchannel.write(buf); Read data from the Buffer yourself, using one of the get() methods. byte abyte = buf.get();

16 ScaJering Reads ByteBuffer header = ByteBuffer.allocate(128); ByteBuffer body = ByteBuffer.allocate(1024); ByteBuffer[] bufferarray = { header, body }; channel.read(buffers);

17 Gathering Writes ByteBuffer header = ByteBuffer.allocate(128); ByteBuffer body = ByteBuffer.allocate(1024); //write data into buffers ByteBuffer[] bufferarray = { header, body }; channel.write(buffers);

18 NIO CHANNELS

19 Channels FileChannel DatagramChannel SocketChannel ServerSocketChannel

20 File Channel Has current posiaon in its file Has current size of its file Can read/write bytes at absolute posiaons A region can be mapped directly into memory Updates can be forced out to the disk Can transfer bytes directly to/from a channel A region can be locked against other accesses

21 Obtaining File Channel Instance FileInputStream.getChannel() FileOutputStream.getChannel() RandomAccessFile.getChannel()

22 Closing File Channel FileChannel.close() Also closes the object whose getchannel() method returned the Channel FileInputStream/FileOutputStream/ RandomAccessFile.close() Also closes the Channel

23 Transfer From RandomAccessFile fromfile = null; RandomAccessFile tofile = null; try { fromfile = new RandomAccessFile("fromFile.txt", "rw"); tofile = new RandomAccessFile("toFile.txt", "rw"); FileChannel fromchannel = fromfile.getchannel(); FileChannel tochannel = tofile.getchannel(); tochannel.transferfrom(fromchannel, 0, fromchannel.size()); } finally { IOUQls.closeQuietly(fromFile); IOUQls.closeQuietly(toFile); }

24 Transfer To RandomAccessFile fromfile = null; RandomAccessFile tofile = null; try { fromfile = new RandomAccessFile("fromFile.txt", "rw"); tofile = new RandomAccessFile("toFile.txt", "rw"); FileChannel fromchannel = fromfile.getchannel(); FileChannel tochannel = tofile.getchannel(); fromchannel.transferto(0, fromchannel.size(), tochannel); } finally { IOUQls.closeQuietly(fromFile); IOUQls.closeQuietly(toFile); }

25 Socket Channel SocketChannel sc = SocketChannel.open(); try { sc.connect(new InetSocketAddress("localhost", 80));... } finally { sc.close(); }

26 Transfer Socket To File FileChannel fc = new RandomAccessFile("out", "rw").getchannel(); try { int pos = 0; long bytesread; while ((bytesread = fc.transferfrom(sc, pos, 4096)) > 0) pos += bytesread; } finally { fc.close(); }

27 Server Socket Channel ServerSocketChannel ssc = ServerSocketChannel.open(); ssc.socket().bind(new InetSocketAddress(80)); while (true) { } SocketChannel sc = ssc.accept(); handle(sc);

28 WriQng To Datagram Channel DatagramChannel channel = DatagramChannel.open(); String data = "Hello"; ByteBuffer buf = ByteBuffer.wrap(data.getBytes()); int bytessent = channel.send( buf, new InetSocketAddress("localhost", 9999)); channel.connect( new InetSocketAddress("localhost", 9999)); int bytessent = channel.write(buf);

29 Reading From Datagram Channel DatagramChannel channel = DatagramChannel.open(); ByteBuffer buf = ByteBuffer.allocate(1024); buf.clear(); channel.socket().bind(new InetSocketAddress(9999)); SocketAddress sa = channel.receive(buf); channel.connect( new InetSocketAddress("localhost", 8888)); int bytesreceived = channel.read(buf);

30 NIO SELECTORS

31 Selectors A Selector allows a single thread to handle mulqple Channel's.

32 Channel Events Connect Accept Read Write

33 Registering Channel Channel Selector Interest Set (events) Ready Set (events) An ajached object (opqonal)

34 Registering Datagram Channels Selector selector = Selector.open(); for (int port : ports) { DatagramChannel dc = DatagramChannel.open(); dc.configureblocking(false); dc.bind(new InetSocketAddress(port)); dc.register(selector, SelecAonKey.OP_READ); }

35 SelecQng Datagram Channels while (true) { } selector.select(); for (Iterator<SelecQonKey> it = } selector.selectedkeys().iterator(); it.hasnext();) { SelecQonKey sk = it.next(); DatagramChannel dc = (DatagramChannel) sk.channel(); // read channel it.remove();

36 Registering Server Socket Channel Selector selector = Selector.open(); ServerSocketChannel ssc = ServerSocketChannel.open(); ssc.configureblocking(false); ssc.bind(new InetSocketAddress(4000)); ssc.register(selector, SelecAonKey.OP_ACCEPT);

37 SelecQng (Server) Socket Channels while (true) { selector.select(); for (Iterator<SelecQonKey> it = selector.selectedkeys().iterator(); it.hasnext();) { SelecQonKey key = it.next(); if (key.isreadable()) read(key); else if (key.isacceptable()) accept(key); it.remove(); } }

38 Reading Socket Channel void read(selecqonkey key) { SocketChannel sc = (SocketChannel) key.channel(); ByteBuffer buf = ByteBuffer.allocate(1024); int bytesread = sc.read(buf); if (bytesread == - 1) sc.close(); else handle(buf); }

39 AccepQng Socket Channel void accept(selecqonkey key) { ServerSocketChannel ssc = (ServerSocketChannel) key.channel(); } SocketChannel sc = ssc.accept(); sc.configureblocking(false); Selector selector = key.selector(); sc.register(selector, SelecAonKey.OP_READ);

40 NIO.2 (FILE I/O)

41 Based On File I/O (Featuring NIO.2) Java Tutorial hjp://docs.oracle.com/javase/tutorial/ essenqal/io/fileio.html

42 What is NIO.2? File Paths File OperaQons Managing Metadata Walking the File Tree Finding Files Watching a Directory for Changes

43 Other Benefits Supports symbolic links Improved support for relaqve paths Improved support for directory lisqngs Improved error handling

44 Paths Paths.get("c:\\example\\data\\input.txt"); Paths.get("/example/data/input.txt"); Paths.get("example/data/input.txt"); Paths.get("example\\data\\input.txt"); Paths.get("example", "data", "input.txt"); Paths.get("/", "example", "data", "input.txt"); Paths.get( URI.create("file:/example/data/input.txt"));

45 Path class Path { String tostring() Path getfilename() Path getname(int index) int getnamecount() Path subpath(int beginindex, int endindex) Path getparent() Path getroot() }

46 Path (2) class Path { Path normalize() boolean isabsolute() Path toabsolutepath() Path resolve(path other) Path relaqvize(path other) File tofile() URI touri() }

47 Path (3) Path torealpath(linkopqon... opqons) throws IOExcepQon enum LinkOpQon { NOFOLLOW_LINKS; } apath.torealpath() follows symbolic links apath.torealpath(linkopqon.nofollow_links) doesn t follow symbolic links

48 Checking Files Files { boolean exists(path path, LinkOpQon... opqons) boolean notexists(path path, LinkOpQon... opqons) boolean isreadable(path path) boolean iswritable(path path) boolean isexecutable(path path) boolean issamefile(path path, Path path2) throws IOExcepQon }

49 DeleQng Files Files { void delete(path path) throws IOExcepQon boolean deleteifexists(path path) throws IOExcepQon } May throw NoSuchFileExcepQon DirectoryNotEmptyExcepQon

50 Coping Files Files { } Path copy(path source, Path target, CopyOpQon... opqons) long copy(inputstream in, OutputStream out) long copy(inputstream in, Path target, CopyOpQon... opqons) long copy(path source, OutputStream out)

51 Coping Files (2) enum StandardCopyOpQon implements CopyOpQon { REPLACE_EXISTING, } COPY_ATTRIBUTES, ATOMIC_MOVE; enum LinkOpQon implements CopyOpQon { } NOFOLLOW_LINKS;

52 Moving Files Files { } Path move(path source, Path target, CopyOpQon... OpQons) Supported opqons: REPLACE_EXISTING ATOMIC_MOVE

53 LisQng Directories try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) { for (Path file: stream) System.out.println(file.getFileName()); } catch (IOExcepQon DirectoryIteratorExcepQon x) { } System.err.println(x);

54 Filtering Directory LisQngs DirectoryStream<Path> stream = Files.newDirectoryStream(dir, new Filter<Path>() { boolean accept(path path) { } }); return Files.isDirectory(path); DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.class");

55 Reading and WriQng Files class Files { byte[] readallbytes(path path) } List<String> readalllines(path path, Charset cs) Path write(path p, byte[] bytes, OpenOpQon... oo) Path write(path path, Iterable<? Extends CharSequence> lines, Charset c, OpenOpQon... oo)...

56 NIO.2 FILE METADATA

57 Basic File AJributes Files { long size(path path) boolean isdirectory(path path, LinkOpQon... lo) boolean isregularfile(path path, LinkOpQon... lo) boolean issymboliclink(path path) boolean ishidden(path path) }

58 Last Modified Time FileTime Qme = Files.getLastModifiedTime(path); long millis = Qme.toMillis(); long millis = System.currentTimeMillis(); FileTime Qme = FileTime.fromMillis(millis); Files.setLastModifiedTime(path, Qme);

59 File Owner UserPrincipal owner = Files.getOwner(path); String name = owner.getname(); String name = "James"; UserPrincipal owner = path.getfilesystem(). getuserprincipallookupservice(). lookupprincipalbyname(name); Files.setOwner(path, owner);

60 Geng POSIX File Permissions Set<PosixFilePermission> perms = Files.getPosixFilePermissions(path); boolean ownerread = perms.contains( PosixFilePermission.OWNER_READ); System.out.println(perms); System.out.println( PosixFilePermissions.toString(perms));

61 Seng POSIX File Permissions Set<PosixFilePermission> perms = new HashSet<PosixFilePermission>(); perms.add(posixfilepermission.owner_read); Files.setPosixFilePermissions(path, perms); Set<PosixFilePermission> perms = PosixFilePermissions.fromString("rwxr- xr- x"); Files.setPosixFilePermissions(path, perms);

62 POSIX File Permissions OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_WRITE GROUP_EXECUTE OTHERS_READ OTHERS_WRITE OTHERS_EXECUTE

63 Single File AJributes Files { } Object geta^ribute(path path, String ajribute, LinkOpQon... opqons) Path seta^ribute(path path, String ajribute, Object value, LinkOpQon... opqons)

64 Reading File AJributes Files { } <A extends BasicFileAJributes> A reada^ributes( Path path, Class<A> type, LinkOpQon... opqons)

65 File AJribute Views Files { } <V extends FileAJributeView> V getfilea^ributeview( Path path, Class<V> type, LinkOpQon... opqons)

66 Supported AJributes FileAJributeView BasicFileAJributeView DosFileAJributeView PosixFileAJributeView FileOwnerAJributeView AclFileAJributeView UserDefinedFileAJributeView BasicFileAJributes DosFileAJributes PosixFileAJributes

67 DOS File AJributes DosFileAJributes ajr = Files.readAJributes( path, DosFileAJributes.class); interface DosFileAJributes extends BasicFileAJributes { boolean isreadonly() boolean ishidden() boolean isarchive() boolean issystem() }

68 Summary Mostly basic IO is good enough and it may be even faster than NIO Use NIO for direct file transfers, memory mappings, file locking etc Use NIO Selectors for mulqple sockets with low bandwidth

69 Summary (2) Use NIO.2 File API for faster directory lisqngs bejer metadata listening for changes finding files

70 QUESTIONS?

71 Homework 11 Write a Java program which mirrors a directory (not recursively) 1. Take the source and target directory paths as input arguments. 1. Fail if source directory does not exist. 2. Create the target directory if it doesn't exist.

72 Homework 11 (2) 2. On startup compare directory lisqngs (use java.nio.file.directorystream) and Copy new files from source to target directory. 2. Copy updated (check last modified Qmes) files from source to target directory. 3. Remove files from target directory which have been removed from source directory. 4. Ignore sub directories in both source and target directory.

73 Homework 11 (3) 3. Watch source directory for changes (use java.nio.file.watchservice) and mirror them into the target directory. 1. Exit when the source directory gets removed (watch key is invalid). 4. Use Java 7 File APIs (java.nio.file) instead of the old (java.io.file). 5. Print a message about each file operaqon you make. 6. Source directory must not be altered.