// newio/ChannelCopy.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Copying a file using channels and buffers
// {java ChannelCopy ChannelCopy.java test.txt}
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class ChannelCopy {
  private static final int BSIZE = 1024;
  public static void main(String[] args) {
    if(args.length != 2) {
      System.out.println(
        "arguments: sourcefile destfile");
      System.exit(1);
    }
    try(
      FileChannel in = new FileInputStream(
        args[0]).getChannel();
      FileChannel out = new FileOutputStream(
        args[1]).getChannel()
    ) {
      ByteBuffer buffer = ByteBuffer.allocate(BSIZE);
      while(in.read(buffer) != -1) {
        buffer.flip(); // Prepare for writing
        out.write(buffer);
        buffer.clear();  // Prepare for reading
      }
    } catch(IOException e) {
      throw new RuntimeException(e);
    }
  }
}