问题
I use openfire and smack for presence management in my app. I use phone number as username and wanna get list of registered users that exist in user device contacts list. Is there any way to check users registration state?
回答1:
To determine registered users (just like Whatsapp) you can simply post contact's of user on your server and there you can check which contacts exist in your users table (the table where you keep the entry of new user with his phone number). Based on that data you can reply to your application with those phone numbers which are registered on your service and they can be shown to user in mobile app.
来源：https://stackoverflow.com/questions/40956415/xmpp-smack-and-openfire-get-registration-state-of-group-of-users