import java.nio.channels.ReadableByteChannel;

import java.nio.channels.WritableByteChannel;

import java.nio.channels.Channels;

import java.nio.ByteBuffer;

import java.io.IOException;

public class ChannelDemo{

public static void main(String[] args){

ReadableByteChannel readChannel = Channels.newChannel(System.in);

WritableByteChannel writeChannel = Channels.newChannel(System.out);

try{

int command = (int)(Math.random() * 2);

switch(command){

case 0:

System.err.println("command = " + command + ", use copy(..) method.");

System.err.println();

copy(readChannel, writeChannel);

break;

case 1:

System.err.println("command = " + command + ", use copyAlt(..) method.");

System.err.println();

copyAlt(readChannel, writeChannel);

break;

}

}catch(IOException ioe){

ioe.printStackTrace();

}finally{

try{

readChannel.close();

writeChannel.close();

}catch(IOException ioe){

ioe.printStackTrace();

}

}

}

static void copy(ReadableByteChannel readChannel, WritableByteChannel writeChannel) throws IOException{

ByteBuffer buffer = ByteBuffer.allocateDirect(2048);

while(readChannel.read(buffer) != -1){

buffer.flip();

writeChannel.write(buffer); // maybe not drain the buffer completely.

buffer.compact();

}

// read ended.

buffer.flip();

while(buffer.hasRemaining()){

writeChannel.write(buffer);

}

}

static void copyAlt(ReadableByteChannel readChannel, WritableByteChannel writeChannel) throws IOException{

ByteBuffer buffer = ByteBuffer.allocateDirect(2048);

while(readChannel.read(buffer) !=-1){

buffer.flip();

while(buffer.hasRemaining()){

writeChannel.write(buffer);

}

// Drained the buffer completely now.

buffer.clear();

// Ready for next read process.

}

}

}