How to get registered users from openfire server using smack4.1

Hi,

i am using smack4.1 to make a chat app.

i created some users through android client.

i tried to retrieve all existing users from openfire server. i checked api but unable to find which class is useful  to get all existing users.

Please help me how to retrieve all created users after making the connection to check the duplication of user entries while registration.

Thanks in advance...