NIO FileChannel

NIO提供了比传统的文件访问更好的访问方法，NIO有两个优化的方法：一个是 FIleChannel.transferTo FileChannel.transferFrom，另一个是FileChannel.map，均提供了数据在内核空间的直接移动，减少了内核空间和用户空间的复制损耗

下面是FileChannel.map使用示例：

    public static void main(String[] args) {
        int BUFFER_SIZE = 1024;
        String filename = "teset.db";
        long fileLength = new File(filename).length();
        int bufferCount = 1 + (int) fileLength / BUFFER_SIZE;
        MappedByteBuffer[] buffers = new MappedByteBuffer[bufferCount];
        long remaining = fileLength;
        for (int i=0; i<bufferCount; i++) {
            RandomAccessFile file;
            try {
                file = new RandomAccessFile(filename, "r");
                buffers[i] = file.getChannel().map(FileChannel.MapMode.READ_ONLY, i*BUFFER_SIZE, (int) Math.min(remaining, BUFFER_SIZE));
            } catch (Exception e) {
                e.printStackTrace();
            }
            remaining -= BUFFER_SIZE;
        }
    }