public Collection<NodeSubscription> getSubscriptions(JID owner) {
        Collection<NodeSubscription> subscriptions = new ArrayList<>();
        for (NodeSubscription subscription : subscriptionsByID.values()) {
            if (owner.equals(subscription.getOwner())) {
                subscriptions.add(subscription);
            }
        }
        getLogger().trace("Got {} subscription(s) for '{}'", subscriptions.size(), owner);
        return subscriptions;
    }
Returns the list of subscriptions owned by the specified user. The subscription owner
may have more than one subscription based on {@link #isMultipleSubscriptionsEnabled()}.
Each subscription may have a different subscription JID if the owner wants to receive
notifications in different resources (or even JIDs).

@param owner the owner of the subscriptions.
@return the list of subscriptions owned by the specified user.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/Node.java