java FileChannel用法

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
import java.io.File;
import java.nio.MappedByteBuffer;

public class tmp
{
        public static void main(String args[]) throws Exception
        {
                File src = new File("a.out");
                File dst = new File("b.out");
                FileChannel in = new FileInputStream(src).getChannel();
                FileChannel out = new FileOutputStream(dst).getChannel();

                MappedByteBuffer buf = in.map(FileChannel.MapMode.READ_ONLY, 0, src.length());
                out.write(buf);
        }
}