java nio 文件传输

import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class LargeMappedFiles {
    static int length = 0x8FFFFFF; // 128 Mb

    public static void main(String[] args) throws Exception {
        MappedByteBuffer out = new RandomAccessFile("test.dat", "rw")
                .getChannel().map(FileChannel.MapMode.READ_WRITE, 0, length);
        for (int i = 0; i < length; i++)
            out.put((byte) 'x');
        System.out.println("Finished  writing ");
        for (int i = length / 2; i < length / 2 + 6; i++)
            System.out.print((char) out.get(i)); // read file
    }
}