FTP Download with design patterns in Java

I have to do ftp download process 1) Check ftp files in each intervals 2) If any files have placed in ftp check whether file has completely uploaded in ftp or else check after some time(Here I'm planning to use observer design pattern) 3)Once file is completely placed, By using one of the BlockingQueue will start download.(please suggest which blocking queue should be used) 4)And if download is stopped because of some issue resume stopped one.

There can be multiple files, that also downloaded parallely Please help in the above scenario with right design patterns and steps