import java.io.RandomAccessFile;

import java.io.IOException;

import java.nio.channels.FileChannel;

import java.nio.ByteBuffer;

public class FileChannelDemo{

public static void main(String[] args) throws IOException{

RandomAccessFile file = new RandomAccessFile("FileChannelDemo.temp", "rw");

FileChannel fileChannel = file.getChannel();

long pos;

System.out.println("Underlying file position: " + (pos = fileChannel.position())

+ ", file size: " + fileChannel.size());

String msg = null;

if(args.length > 0){

msg = args[0];

}else{

msg = "This is a demo message for test.";

}

ByteBuffer buffer = ByteBuffer.allocateDirect(msg.length()*2); // char is two byte long.

buffer.asCharBuffer().put(msg); // CharBuffer used as a view buffer, its change is visible to the backing ByteBuffer.

fileChannel.write(buffer);

// recommend the operating system to commit the written data to storage device, including metadata.

fileChannel.force(true);

System.out.println("Underlying file position: " + fileChannel.position()

+ ", file size: " + fileChannel.size());

buffer.clear(); // prepare for refresh use as newly created buffer.

fileChannel.position(pos); // prepare for read operation

fileChannel.read(buffer);

// Inspect the buffer data after read.

buffer.flip();

while(buffer.hasRemaining()){

System.out.print(buffer.getChar()); // retrieve 2 bytes per time.

}

}

}