分片与并发结合，将一个大文件分割成多块，并发上传，极大地提高大文件的上传速度。 当网络问题导致传输错误时，只需要重传出错分片，而不是整个文件。另外分片传输能够更加实时的跟踪上传进度。(Fragment and concurrent combination, a large file is divided into many blocks, concurrent upload, greatly improve the upload speed of large files. When a ne