快速创建3G大文件，耗时不到1S，写下载器可以用到。
Path path = Paths.
get(
"d:\\a.txt");
byte[] output =
new byte[
1];
ByteBuffer bf = ByteBuffer.
wrap(output);
try(FileChannel fc = FileChannel.
open(path,
WRITE,
CREATE)) {
fc.position((
3L <<
30) -
1);
fc.write(bf);
}
catch (IOException e) {
e.printStackTrace();
}
