public abstract class Widget {
 
 	protected List<Object> widgets = new ArrayList<Object>();
 
 	public abstract boolean register(Object object);
 	public abstract String initialize();
 }
 

public class DatePicker extends Widget {
 
 	@Override
 	public String initialize() {
 		StringBuilder sb = new StringBuilder("");
 		if (widgets.size() > 0)	{
 			sb.append("<script language='javascript'>\n");
 			sb.append("  datePickerController.create();\n");
 			sb.append("  datePickerController.datePickers[\""+ datePickersToString() +"\"];\n");
 			sb.append("</script>");
 		}
 		return sb.toString();
 	}
 
 	@Override
 	public boolean register(Object object) {
 		return widgets.add(object.toString());
 	}
 
 	private String datePickersToString() {
 		StringBuilder sb = new StringBuilder("");
 		for (Object obj : widgets) {
 			sb.append(obj.toString());
 			sb.append(" ");
 		}
 		return sb.deleteCharAt(sb.length()-1).toString();
 	}
 
 }
 
 

public class RegisterWidgetsTag extends BaseTag implements LogicalTag {
 
 	private static Map<Object, Widget> widgets = new HashMap<Object, Widget>();
 
 	public static void registerWidget(Object object, Class widgetClass) throws IllegalAccessException, InstantiationException {
 		Widget widget;
 		if (!widgets.containsKey(object)) {
 			widget = getRegistredWidget(widgetClass);
 			if ( widget != null) {
 				widget.register(object);
 				return;
 			}
 			widget = (Widget) widgetClass.newInstance();
 			widgets.put(object, widget);
 			widget.register(object);
 		}
 	}
 
 	@Override
 	protected void doComponent() throws Exception {
 		Set<Object> keySet = widgets.keySet();
 		for (Object key : keySet) {
 			getOut().println(widgets.get(key).initialize());
 		}
 		widgets.clear();
 	}
 
 	private static Widget getRegistredWidget(Class widgetClass) {
 		Collection<Widget> widgetList = widgets.values();
 		for (Widget widget : widgetList) {
 			if (widget.getClass() == widgetClass)
 				return widget;
 		}
 		return null;
 	}
 
 }
 

RegisterWidgetsTag.registerWidget(name, DatePicker.class);