The following small program throws an assertion error when asserts
are enabled. I don't see anything wrong with the program and it clearly
finds the file properly so I think the bug is in NIO

import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public class Map {

   public static void main(String [] args) {
       try {
RandomAccessFile raf = new RandomAccessFile("/etc/passwd", "r");
FileChannel fc = raf.getChannel();
long fileSize = fc.size();
System.out.println("filesize = " + fileSize);
MappedByteBuffer mapBuf =
fc.map(FileChannel.MapMode.READ_ONLY, 0l, fileSize);
       } catch (Throwable t) {
t.printStackTrace();
       }
   }
}

% /import/java/jdk1.5/solaris-sparc/bin/java -esa Map
filesize = 467
java.lang.AssertionError
at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:745)
at Map.main(Map.java:13)