FileChannel ByteBuffer和散列文件

3条建议：

1）每次读取后清除缓冲区

while (fc.read(bbf) != -1) {    md.update(bbf.array(), 0, bytes);    bbf.clear();}

2）不要同时关闭fc和fis，这是多余的，关闭fis就足够了。FileInputStream.close API说：

If this stream has an associated channel then the channel is closed as well.

3）如果您想通过使用FileChannel来提高性能

ByteBuffer.allocateDirect(1024);