Fastest way to incrementally read a large file

Question

When given a buffer of MAX_BUFFER_SIZE, and a file that far exceeds it, how can one:

1. Read the file in blocks of MAX_BUFFER_SIZE?
2. Do it as fast as poss

Answer 1

If you want to make your first example faster

FileChannel inChannel = new FileInputStream(fileName).getChannel();
ByteBuffer buffer = ByteBuffer.allocateDirect(CAPACITY);

while(inChannel.read(buffer) > 0)
    buffer.clear(); // do something with the data and clear/compact it.

inChannel.close();

If you want it to be even faster.

FileChannel inChannel = new RandomAccessFile(fileName, "r").getChannel();
MappedByteBuffer buffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
// access the buffer as you wish.
inChannel.close();

This can take 10 - 20 micro-seconds for files up to 2 GB in size.