How to copy a file on the FTP server to a directory on the same server in Java?

Question

I\'m using Apache Commons FTP to upload a file. Before uploading I want to check if the file already exists on the server and make a backup from it to a backup directory on

Answer 1

There's no standard way to duplicate a remote file over FTP protocol. Some FTP servers support proprietary or non-standard extensions for this though.

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So if your are lucky that your server is ProFTPD with mod_copy module, you can use FTP.sendCommand to issue these two commands:

f.sendCommand("CPFR sourcepath");
f.sendCommand("CPTO targetpath");

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The second possibility is that your server allows you to execute arbitrary shell commands. This is even less common. If your server supports this you can use SITE EXEC command:

SITE EXEC cp -p sourcepath targetpath

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Another workaround is to open a second connection to the FTP server and make the server upload the file to itself by piping a passive mode data connection to an active mode data connection. Implementation of this solution (in PHP though) is shown in FTP copy a file to another place in same FTP.

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If neither of this works, all you can do is to download the file to a local temporary location and re-upload it back to the target location. This is that the answer by @RP- shows.

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See also FTP copy a file to another place in same FTP.