Reading file asynchronously in Java

We all are familiar with reading/writing file in a synchronous way. In Java 7 a new API was added to read/write the contents of the file asynchronously. The API is AsynchronousFileChannel.

also read:

• Java 7.0 Tutorials
• New Features in Java 7.0
• G1 Garbage Collector in Java 7.0

In this example lets look at how to read the contents of the file asynchronously. There are two approaches to read the contents asynchronously:
1. To use Future class to wait for the result of the read operation.
2. To use a callback defined by the CompletionHandler to process the result of the Asynchronous operation.

//Using Future class to read the contents of the file.
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.charset.Charset;
import java.nio.file.*;
import java.util.concurrent.*;

public class AsyncFutureRead {

  public static void main(String[] args) {

    //Buffer to read the contents from the file.
    ByteBuffer buffer = ByteBuffer.allocate(100);

    //The file to read the contents from.
    Path path = Paths.get('D:/tests/test.txt');

    //Creating the asynchronous channel to the file which allows reading and writing of content.
    try(AsynchronousFileChannel asyncChannel = AsynchronousFileChannel.open(path)){

      //Returns a Future instance which can be used to read the contents of the file.
      Future<Integer> fileResult = asyncChannel.read(buffer, 0);

      //Waiting for the file reading to complete.
      while(!fileResult.isDone()){
        System.out.println('Waiting to complete the file reading ...');
      }

      //Print the number of bytes read.
      System.out.println('Number of bytes read: '+fileResult.get());

      //Reset the current position of the buffer to the beginning and the limit to the current position.
      buffer.flip();

      //Decode the contents of the byte buffer.
      System.out.println('Contents of file: ');
      System.out.println(Charset.defaultCharset().decode(buffer));

    }catch(IOException | InterruptedException | ExecutionException ex){
      ex.printStackTrace();
    }
  }
}

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