User Already Exists Exception

If user alredy registered in open fire databse it showing  a message "<error>UserAlreadyExistsException</error>".

My site in joomla CMS and configured with openfire. I want to add some custom code in my site related UserAlreadyExistsException.

Please provide the "UserAlreadyExistsException" functions and parametes, then I will apply and check on my joomla site.

Note : Functions and this parameters of "UserAlreadyExistsException" code.

Please provide ASAP.

Thanks & Regards.