“550 SSL/TLS required on the data channel” using Apache Commons FTPSClient

Question

I have a probleme reading data with FTPClient on a FTP-Server (ProFTPD 1.3.3a) that requires encryption on the data channel. Everything works fine without encryption on an o

Answer 1

You must enable data channel encryption before executing any commands that will transfer data over the data channel (such as LIST does).

Add this to your code after connecting to the server:

// Set protection buffer size
ftpClient.execPBSZ(0);
// Set data channel protection to private
ftpClient.execPROT("P");

At least, this solved my problems (using proftpd).