public static boolean isGroup(JID jid) {
        try {
            return isGroup(jid, false);
        } catch (GroupNotFoundException gnfe) {
            // should not happen because we do not validate the group exists
            Log.error("Unexpected group validation", gnfe);
            return false;
        }
    }
Check a JID to determine whether it represents a group. If the given
JID is an instance of this class, it is a group JID. Otherwise,
calculate the hash to determine whether the JID can be resolved to
a group.

@param jid A JID, possibly representing a group
@return true if the given jid represents a group in the local domain
xmppserver/src/main/java/org/jivesoftware/openfire/group/GroupJID.java