The javadoc for SocketException states that it is
Thrown to indicate that there is an error in the underlying protocol such as a TCP error
In your case it seems that the connection has been closed by the server end of the connection. This could be an issue with the request you are sending or an issue at their end.
To aid debugging you could look at using a tool such as Wireshark to view the actual network packets. Also, is there an alternative client to your Java code that you could use to test the web service? If this was successful it could indicate a bug in the Java code.
As you are using Commons HTTP Client have a look at the Common HTTP Client Logging Guide. This will tell you how to log the request at the HTTP level.