The program reads and prints the contents a text file in the default directory.
To read the contents of a different file, change the path of the file in the main() method.
import static java.nio.file.StandardOpenOption.READ; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.AsynchronousFileChannel; import java.nio.channels.CompletionHandler; import java.nio.charset.Charset; import java.nio.file.Path; import java.nio.file.Paths; class Attachment { public Path path; public ByteBuffer buffer; public AsynchronousFileChannel asyncChannel; } // An inner class to handle completion of the asynchronous read operation class ReadHandler implements CompletionHandler<Integer, Attachment> { @Override/* ww w . j a v a 2s .c o m*/ public void completed(Integer result, Attachment attach) { System.out.format("%s bytes read from %s%n", result, attach.path); System.out.format("Read data is:%n"); byte[] byteData = attach.buffer.array(); Charset cs = Charset.forName("UTF-8"); String data = new String(byteData, cs); System.out.println(data); try { // Close the channel attach.asyncChannel.close(); } catch (IOException e) { e.printStackTrace(); } } @Override public void failed(Throwable e, Attachment attach) { System.out.format("Read operation on %s file failed." + "The error is: %s%n", attach.path, e.getMessage()); try { // Close the channel attach.asyncChannel.close(); } catch (IOException e1) { e1.printStackTrace(); } } } public class Main { public static void main(String[] args) { Path path = Paths.get("data.txt"); try { // Get an async channel AsynchronousFileChannel afc = AsynchronousFileChannel.open(path, READ); // Get a completion handler ReadHandler handler = new ReadHandler(); // Get the data size in bytes to read int fileSize = (int) afc.size(); ByteBuffer dataBuffer = ByteBuffer.allocate(fileSize); // Prepare the attachment Attachment attach = new Attachment(); attach.asyncChannel = afc; attach.buffer = dataBuffer; attach.path = path; // Perform the asynchronous read operation afc.read(dataBuffer, 0, attach, handler); try { // Let the thread sleep for five seconds, // to allow the asynchronous read to complete System.out.println("Sleeping for 5 seconds..."); Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Done..."); } catch (IOException e) { e.printStackTrace(); } } }