public static String getUserName(JID entity, String defaultName) throws UserNotFoundException {
        if (server.isLocal(entity)) {
            // Contact is a local entity so search for his user name
            User localUser = UserManager.getInstance().getUser(entity.getNode());
            return !localUser.isNameVisible() || "".equals(localUser.getName()) ? entity.getNode() : localUser.getName();
        } else {
            UserNameProvider provider = providersByDomain.get(entity.getDomain());
            if (provider != null) {
                return provider.getUserName(entity);
            }
            // TODO Request vCard to the remote server/component and return the name as
            // TODO defined in the vCard. We might need to cache this information to avoid
            // TODO high traffic.

            // Return the jid itself as the username
            return defaultName;
        }
    }
Returns the name of the XMPP entity. If the entity is a local user then the User's name
will be returned. However, if the user is not a local user then check if there exists a
UserNameProvider that provides name for the specified domain. If none was found then
the vCard of the entity might be requested and if none was found then a string
representation of the entity's JID will be returned.

@param entity      the JID of the entity to get its name.
@param defaultName default name to return when no name was found.
@return the name of the XMPP entity.
@throws UserNotFoundException if the jid belongs to the local server but no user was
                              found for that jid.
xmppserver/src/main/java/org/jivesoftware/openfire/user/UserNameManager.java