MappedByteBuffer

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;

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

public static void main(String[] args) throws Exception {
Test t = new Test();
t.testByteBufferRead();
t.testMappedByteBufferRead();
}

public void testByteBufferRead() {
try {
int length = 0XFFFFFFF;
MappedByteBuffer out = null;
try {
out = new RandomAccessFile("c:/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");
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
// Obtain a channel
ReadableByteChannel channel = new FileInputStream("c:/test.dat")
.getChannel();

// Create a direct ByteBuffer; see also e158 Creating a ByteBuffer
ByteBuffer buf = ByteBuffer.allocateDirect(10);

int numRead = 0;
while (numRead >= 0) {
// read() places read bytes at the buffer's position so the
// position should always be properly set before calling read()
// This method sets the position to 0
buf.rewind();

// Read bytes from the channel
numRead = channel.read(buf);

// The read() method also moves the position so in order to
// read the new bytes, the buffer's position must be set back to
// 0
buf.rewind();

// Read bytes from ByteBuffer; see also
// e159 Getting Bytes from a ByteBuffer
for (int i = 0; i < 10; i++) {
byte b = buf.get(i);
System.out.println((char) b);
}
}
} catch (Exception e) {
e.printStackTrace();
}

}

public void testMappedByteBufferRead() {
int length = 0XFFFFFFF;
MappedByteBuffer out = null;
try {
out = new RandomAccessFile("c:/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");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
for (int i = length / 2; i < length / 2 + 6; i++)
System.out.print((char) out.get(i)); // read file
}
}