updatecollection, lightbox, retrieve list from server


I have a ‘select’ section on lightbox. I need update select list from server.
this is my lightbox sections:

				{name:"description", height:130, map_to:"text", type:"textarea" , focus:true},
	        	{name:"client_id", height:21, map_to:"client_id", type:"select",options:scheduler.serverList("client_id"), button:"newClientButton"},
				{name:"location", height:43, type:"textarea", map_to:"details" },
				{name:"time", height:72, type:"time", map_to:"auto"},
	        	{name:"user_id", height:21, map_to:"user_id", type:"select",options:scheduler.serverList("user_id"), cache:false}

I suspect it possible to do by using updateCollection(‘client_id’, new_list)
Please show how to retrieve updated list from server. I.e. how to get new_list object from
On server side I have Java basic connector

public class Basic_connector extends ConnectorServlet {

	private static final long serialVersionUID = 1L;
	protected void configure() {
		Connection conn= ( new DataBaseConnection()).getConnection();
		FormConnector c = new FormConnector(conn, DBType.PostgreSQL);
		c.render_table("clients", "id", "name, surname");

Best regards.