I've had success with Sysinternals Process Explorer. With this, you can search to find what process(es) have a file open, and you can use it to close the handle(s) if you want. Of course, it is safer to close the whole process. Exercise caution and judgement.
To find a specific file, use the menu option Find->Find Handle or DLL... Type in part of the path to the file. The list of processes will appear below.
If you prefer command line, Sysinternals suite includes command line tool Handle, that lists open handles.
Examples
c:\Program Files\SysinternalsSuite>handle.exe |findstr /i "e:\" (finds all files opened from drive e:\"c:\Program Files\SysinternalsSuite>handle.exe |findstr /i "file-or-path-in-question"
Short answer: you can't. Ports below 1024 can be opened only by root. As per comment - well, you can, using CAP_NET_BIND_SERVICE, but that approach, applied to java bin will make any java program to be run with this setting, which is undesirable, if not a security risk.
The long answer: you can redirect connections on port 80 to some other port you can open as normal user.
Run as root:
# iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080
As loopback devices (like localhost) do not use the prerouting rules, if you need to use localhost, etc., add this rule as well (thanks @Francesco):
# iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 80 -j REDIRECT --to-ports 8080
NOTE: The above solution is not well suited for multi-user systems, as any user can open port 8080 (or any other high port you decide to use), thus intercepting the traffic. (Credits to CesarB).
EDIT: as per comment question - to delete the above rule:
# iptables -t nat --line-numbers -n -L
This will output something like:
Chain PREROUTING (policy ACCEPT)
num target prot opt source destination
1 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:8080 redir ports 8088
2 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 redir ports 8080
The rule you are interested in is nr. 2, so to delete it:
# iptables -t nat -D PREROUTING 2
Best Answer
Use a client that can resume such as WinSCP.
Or BitTorrent on a private tracker. Bonus: built in verification of all the chunks.
If you still would like multi part archives, there are multiple tools capable of doing that such as 7zip. Multi part archives generally require an archive program at at both ends that can handle the format. I'm sure there are ways to do the equivalent of GNU coreutils
spliton Windows, I don't have the PowerShell handy of how to do it.