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Back to the Future with Java 7Martijn Verburg

(@karianna, @java7developer)

http://www.java7developer.com

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NIO.2 - New I/O version 2

Is aimed at simplifying I/O in Java

A new file system and path abstraction– Based on java.nio.file.Path

– Bulk access to file attributes

– File system specific support (e.g. Symbolic links)

– Extra providers (e.g. zip files treated as normal files)

Asynchronous (non-blocking) I/O– For sockets and files

– Mainly utilises java.util.concurrent.Future

Socket/Channel construct– Binding, options and multicast

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NIO.2 - Path

java.nio2.file.Path interface– Typically represents a file on a file system

– normalize() method removes constructs such as . and .. in a Path

– relativize(Path) constructs relative Path between this path and the one given

– Lots of other expected methods defined in the interface • Dealing with real path, absolute path etc

– Can convert java.io.File objects• Via the public Path toPath() method

java.nio2.file.Paths– Helper class, provides get(URI) method to return you a Path

• Uses FileSystems helper class under the hood• Uses the default file system unless you specify otherwise

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NIO.2 - Path - Some quick exploration

// Get foobar.txt

Path path = Paths.get("../foobar.txt");

// Normalise the path (get rid of the ..)

Path normalizedPath = path.normalize();

// Get the parent Path of the file

Path parent = path.getParent();

// Get the absolute Path of the file

boolean isAbsolute = path.isAbsolute();

   

// Figure out the relative Path between two filesPath barFile = Paths.get("../../bar.txt")Path pathBetweenFiles = path.relativize(barFile);

// Interoperate with Java.io.File

java.io.File file = path.toFile();4

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NIO.2 - Files

java.nio2.file.Files helper class– Day to day class for performing simple file I/O

Many common methods– copy

– delete

– move

– createDirectory/File/Link

– write

– readAllLines

– walkFileTree (recurse over a directory)

– newInputStream/OutputStream

Combined with try-with-resources makes code concise

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NIO.2 - Files - Some quick exploration

Path timeSheetFile = Paths.get("C:/projects/timesheet.txt");

Path backupDir = Paths.get("H:/projects/");

// Create the backup directory

Files.createDirectory(backupDir);

// Check that the file actually exists

// Don’t follow any symbolic links

boolean fileExists = Files.exists(timeSheetFile,

LinkOption.NOFOLLOW_LINKS);

  // Simple copy with overwriteCopyOption copyOptions = StandardCopyOption.REPLACE_EXISTING;Files.copy(timeSheetFile, timeSheetFileBackup, copyOptions);

// Read all of the linesList<String> lines = Files.readAllLines(timeSheetFile,

Charset.defaultCharset());6

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NIO.2 - Files - Some quick exploration II

// Move a file, copying over its attributes as wellFiles.move(timeSheetFile, backupDir,             StandardCopyOption.REPLACE_EXISTING,             StandardCopyOption.COPY_ATTRIBUTES);     

// Delete a fileFiles.deleteIfExists(timeSheetFile);

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URLStream to file - Java 6

URL url =

new URL("http://www.java7developer.com/blog/?page_id=97");

try (

FileOutputStream fos =

new FileOutputStream(new File("output.txt"));

InputStream is = url.openStream() )

{

byte[] buf = new byte[4096];

int len;

while ((len = is.read(buf)) > 0)

{

fos.write(buf, 0, len);

}

} catch (IOException e)

{

e.printStackTrace();

} 8

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URL stream to file in Java 7

// Ignoring the MalformedURLException

URL url =

new URL("http://www.java7developer.com/blog/?page_id=97");

try (InputStream in = url.openStream())

{

Files.copy(in, Paths.get("output.txt"));

}

catch(IOException ex)

{

ex.printStackTrace();

}

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NIO.2 - Asynchronous I/O

The ability to perform read/write operations in the background– Without having to write your own java.util.concurrent code

Is available for:– file I/O (AsynchronousFileChannel)

– networking I/O (AsynchronousSocketChannel)• And AsynchronousServerSocketChannel

Can work in two styles– Future based (order coffee, do something else, collect coffee)

– Callbacks (order coffee, do something else, have coffee thrown at you)

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NIO.2 - Future based file I/O example

try {

Path file = Paths.get("/usr/karianna/foobar.txt");

AsynchronousFileChannel channel =

AsynchronousFileChannel.open(file);

ByteBuffer buffer = ByteBuffer.allocate(100_000_000_000);

Future<Integer> result = channel.read(buffer, 0);

while(!result.isDone()) {

System.out.println("Do some other stuff");

}

Integer bytesRead = result.get();

} catch (IOException | ExecutionException | InterruptedException e)

{

// Deal with exception

}

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NIO.2 - Callback based file I/O example

try {

Path file = Paths.get("/usr/karianna/foobar.txt");

AsynchronousFileChannel channel = AsynchronousFileChannel.open(file);

ByteBuffer buffer = ByteBuffer.allocate(100_000_000_000);

channel.read(buffer, 0, buffer,

new CompletionHandler<Integer, ByteBuffer>() {

    public void completed(Integer result, ByteBuffer attachment) {

        System.out.println("Bytes read [" + result + "]");

        }

        public void failed(Throwable exception, ByteBuffer attachment) {

        // Deal with exception

        }

   });

} catch (IOException e) {

    // Deal with exception

}

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Thanks for listening!(http://www.java7developer.com)

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