private void savePublicGroupsInCache(final HashSet<String> groupNames) {
        synchronized (sharedGroupMetaCache) {
            sharedGroupMetaCache.put(PUBLIC_GROUPS, groupNames);
        }
    }
Returns a custom {@link Map} that updates the database whenever
a property value is added, changed, or deleted.

@param group The target group
@return The properties for the given group
xmppserver/src/main/java/org/jivesoftware/openfire/group/AbstractGroupProvider.java