I must answer myself. One can add a
ProtocolCommandListener<http://commons.apache.org/net/api-3.1/org/apache/commons/net/ProtocolCommandListener.html>
to
the FTPClient (which inherits from SocketClient)

2012/8/15 Raffaele Sgarro <raffaelesgarro@gmail.com>

> I was looking for a way to enable verbose logging for commons-net
> (specifically, I'm using the FTP library), but I can't find anything
> online, and a quick tour of the sources didn't help me. Can anybody tell me
> if such an option exist? For example, with Apache HTTP client one can
> easily examine all the raw socket communication just by setting the log
> level to DEBUG and configuring an appender.
>
> It would be better if commons-net had this feature, instead of cluttering
> client code with endless series of System.out.println(replyText)
>