@Override
    public Collection<String> getServerHostnames() {
        Set<String> domains = new HashSet<>();
        for (DomainPair pair : serversCache.keySet()) {
            domains.add(pair.getRemote());
        }
        return domains;
    }
Gets the non-negative session from a minimal priority.

@param sessions The sessions.
@param min      The minimal priority.
@return The filtered sessions.
xmppserver/src/main/java/org/jivesoftware/openfire/spi/RoutingTableImpl.java