BigByteBuffer.java

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * BigByteBuffer allows mmaping files larger than Integer.MAX_VALUE bytes.
 */
public class BigByteBuffer {
    private static int OVERLAP = Integer.MAX_VALUE / 2;
    private final List<ByteBuffer> buffers;

    /**
     * mmap the file and return a BigByteBuffer for it.
     * @param file the file to mmap
     * @throws java.io.IOException if there is an error reading the file
     */
    public BigByteBuffer(File file) throws IOException {
        this(new RandomAccessFile(file, "r"));
    }

    /**
     * mmap the file and return a BigByteBuffer for it.
     * @param file the file to mmap
     * @throws java.io.IOException if there is an error reading the file
     */
    public BigByteBuffer(RandomAccessFile file) throws IOException {
        long length = file.length();

        if (length == 0) {
            throw new IllegalArgumentException("File is empty");
        }

        buffers = new ArrayList<ByteBuffer>();
        for (long i = 0; i < length; i += OVERLAP) {
            buffers.add(file.getChannel().map(FileChannel.MapMode.READ_ONLY, i, Math.min(length - i, Integer.MAX_VALUE)));
        }
    }

    /**
     * Wrap a ByteBuffer. Used for testing.
     * @param buffer the buffer to wrap
     */
    public BigByteBuffer(ByteBuffer buffer) {
        buffers = Arrays.asList(buffer);
    }

    /**
     * Return a ByteBuffer starting at the specified location in the file
     * @param position the starting position in the file
     * @return ByteBuffer starting at the location in the file
     */
    public ByteBuffer get(long position) {
        ByteBuffer buffer = buffers.get((int) (position / OVERLAP));
        buffer  = buffer.duplicate();
        buffer.position((int) (position % OVERLAP));
        return buffer;
    }
}