Java I/O How to - Create a very large file using mapping

Question

We would like to know how to create a very large file using mapping.

Answer

 //from  ww  w.ja  v  a  2s.c o  m
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class MainClass {
  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));
  }
}

The code above generates the following result.