VaadinServlet is configured in the WebConfig class. The UI implementation is realized in the VaadinUI class. For reference, the following is the implementation of the VaadinUI class:

@Title("Call Browser")
public class VaadinUI extends UI {

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        VerticalLayout mainLayout = new VerticalLayout();
        mainLayout.addComponentsAndExpand(new CallsBrowser());
        setContent(mainLayout);
    }
}

Notice how the UI consists of a VerticalLayout that contains only a CallsBrowser component. We'll start with the following implementation of the CallsBrowser custom component:

public class CallsBrowser extends Composite {

    public CallsBrowser() {
        TextField filter = new TextField();
        filter.setPlaceholder("Client / Phone / City");
        filter.focus();

        Button search = new Button(VaadinIcons.SEARCH);
        search.setClickShortcut(ShortcutAction.KeyCode.ENTER);

        Button clear = new Button(VaadinIcons.CLOSE_SMALL);

        CssLayout filterLayout = new CssLayout(filter, search, clear);
        filterLayout.addStyleName(ValoTheme.LAYOUT_COMPONENT_GROUP);

        Label countLabel = new Label();
        countLabel.addStyleNames(
                ValoTheme.LABEL_LIGHT, ValoTheme.LABEL_SMALL);

        HorizontalLayout headerLayout = new HorizontalLayout(
                filterLayout, countLabel);
        headerLayout.setComponentAlignment(countLabel, Alignment.MIDDLE_LEFT);

        Grid<Call> grid = new Grid<>(Call.class);
        grid.setColumns("id", "client", "phoneNumber", "city", "startTime",
                "duration", "status");
        grid.setSizeFull();

        VerticalLayout mainLayout = new VerticalLayout(headerLayout);
        mainLayout.setMargin(false);
        mainLayout.addComponentsAndExpand(grid);
        setCompositionRoot(mainLayout);
    }
}

The previous class can be used as a starting point if you want to implement the concepts of this chapter yourself. At this point, the UI doesn't show any data in the Grid and it has no behavior.