@Override
    public void addMember(String groupName, JID user, boolean administrator) throws GroupNotFoundException
    {
        getGroupProvider(groupName).addMember(groupName, user, administrator);
    }
Adds an entity to a group (optional operation).

Implementations should use the bare JID representation of the JID passed as an argument to this method.

@param groupName the group to add the member to
@param user the (bare) JID of the entity to add
@param administrator True if the member is an administrator of the group
@throws UnsupportedOperationException if the provider does not support the operation.
@throws GroupNotFoundException if the provided group name does not refer to an existing group.
xmppserver/src/main/java/org/jivesoftware/openfire/group/GroupMultiProvider.java