3.5.14. Composite Components

A composite component is a component consisting of other components. Like screen fragments, composite components allow you to reuse some presentation layout and logic. We recommend using composite components in the following cases:

  • The component functionality can be implemented as a combination of existing Generic UI components. If you need some non-standard features, create a custom component by wrapping a Vaadin component or JavaScript library, or use Generic JavaScriptComponent.

  • The component is relatively simple and does not load or save data itself. Otherwise, consider creating a screen fragment.

The class of a composite component must extend the CompositeComponent base class. A composite component must have a single component at the root of the inner components tree. The root component can be obtained using the CompositeComponent.getComposition() method.

Inner components are usually created declaratively in an XML descriptor. In this case, the component class should have the @CompositeDescriptor annotation which specifies the path to the descriptor file. If the annotation value does not start with /, the file is loaded from the component’s class package.

Alternatively, the inner components tree can be created programmatically in a CreateEvent listener.

CreateEvent is sent by the framework when it finishes the initialization of the component. At this moment, if an XML descriptor is used by the component, it is loaded, and getComposition() method returns the root component. This event can be used for any additional initialization of the component or for creating the inner components without XML.

Below we demonstrate the creation of Stepper component which is designed to edit integer values in the input field and by clicking on up/down buttons located next to the field.

Let’s assume the project has com/company/demo base package.

Component layout descriptor

Create an XML descriptor with the component layout in the com/company/demo/web/components/stepper/stepper-component.xml file of the web module:

<composite xmlns="http://schemas.haulmont.com/cuba/screen/composite.xsd"> (1)
    <hbox id="rootBox" width="100%" expand="valueField"> (2)
        <textField id="valueField"/> (3)
        <button id="upBtn"
        <button id="downBtn"
1 - XSD defines the content of the component descriptor
2 - a single root component
3 - any number of nested components
Component implementation class

Create the component implementation class in the same package:

package com.company.demo.web.components.stepper;

import com.haulmont.bali.events.Subscription;
import com.haulmont.cuba.gui.components.*;
import com.haulmont.cuba.gui.components.data.ValueSource;
import com.haulmont.cuba.web.gui.components.*;

import java.util.Collection;
import java.util.function.Consumer;

@CompositeDescriptor("stepper-component.xml") (1)
public class StepperField
        extends CompositeComponent<HBoxLayout> (2)
        implements Field<Integer>, (3)
                    CompositeWithCaption, (4)
                    CompositeWithContextHelp {

    public static final String NAME = "stepperField"; (5)

    private TextField<Integer> valueField; (6)
    private Button upBtn;
    private Button downBtn;

    private int step = 1; (7)

    public StepperField() {
        addCreateListener(this::onCreate); (8)

    private void onCreate(CreateEvent createEvent) {
        valueField = getInnerComponent("valueField");
        upBtn = getInnerComponent("upBtn");
        downBtn = getInnerComponent("downBtn");

        upBtn.addClickListener(clickEvent -> updateValue(step));
        downBtn.addClickListener(clickEvent -> updateValue(-step));

    private void updateValue(int delta) {
        Integer value = getValue();
        setValue(value != null ? value + delta : delta);

    public int getStep() {
        return step;

    public void setStep(int step) {
        this.step = step;

    public boolean isRequired() { (9)
        return valueField.isRequired();

    public void setRequired(boolean required) {

    public String getRequiredMessage() {
        return valueField.getRequiredMessage();

    public void setRequiredMessage(String msg) {

    public void addValidator(Consumer<? super Integer> validator) {

    public void removeValidator(Consumer<Integer> validator) {

    public Collection<Consumer<Integer>> getValidators() {
        return valueField.getValidators();

    public boolean isEditable() {
        return valueField.isEditable();

    public void setEditable(boolean editable) {

    public Integer getValue() {
        return valueField.getValue();

    public void setValue(Integer value) {

    public Subscription addValueChangeListener(Consumer<ValueChangeEvent<Integer>> listener) {
        return valueField.addValueChangeListener(listener);

    public void removeValueChangeListener(Consumer<ValueChangeEvent<Integer>> listener) {

    public boolean isValid() {
        return valueField.isValid();

    public void validate() throws ValidationException {

    public void setValueSource(ValueSource<Integer> valueSource) {

    public ValueSource<Integer> getValueSource() {
        return valueField.getValueSource();
1 - the @CompositeDescriptor annotation specifies the path to the component layout descriptor which is located in the class package.
2 - the component class extends CompositeComponent parameterized by the type of the root component.
3 - our component implements the Field<Integer> interface because it is designed to display and edit an integer value.
4 - a set of interfaces with default methods to implement standard Generic UI component functionality.
5 - name of the component which is used to register the component in ui-component.xml file to be recognized by the framework.
6 - fields containing references to inner components.
7 - component’s property which defines the value of a single click to up/down buttons. It has public getter/setter methods and can be assigned in screen XML.
8 - component initialization is done in the CreateEvent listener.
Component loader

Create the component loader which is needed to initialize the component when it is used in screen XML descriptors:

package com.company.demo.web.components.stepper;

import com.google.common.base.Strings;
import com.haulmont.cuba.gui.xml.layout.loaders.AbstractFieldLoader;

public class StepperFieldLoader extends AbstractFieldLoader<StepperField> { (1)

    public void createComponent() {
        resultComponent = factory.create(StepperField.NAME); (2)
        loadId(resultComponent, element);

    public void loadComponent() {
        String incrementStr = element.attributeValue("step"); (3)
        if (!Strings.isNullOrEmpty(incrementStr)) {
1 - loader class must extend AbstractComponentLoader parameterized by the class of the component. As our component implements Field, use more specific AbstractFieldLoader base class.
2 - create the component by its name.
3 - load the step property value from XML if it is specified.
Registration of the component

In order to register the component and its loader with the framework, create the com/company/demo/ui-component.xml file of the web module:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<components xmlns="http://schemas.haulmont.com/cuba/components.xsd">

Add the following property to com/company/demo/web-app.properties:

cuba.web.componentsConfig = +com/company/demo/ui-component.xml

Now the framework will recognize the new component in XML descriptors of application screens.

Component XSD

XSD is required to use the component in screen XML descriptors. Define it in the com/company/demo/ui-component.xsd file of the web module:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xs:schema xmlns="http://schemas.company.com/demo/0.1/ui-component.xsd"

    <xs:element name="stepperField">
                <xs:extension base="layout:baseFieldComponent"> (1)
                    <xs:attribute name="step" type="xs:integer"/> (2)
1 - inherit all base field properties.
2 - define an attribute for the step property.
Usage of the component

The following example shows how the component can be used in a screen:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<window xmlns="http://schemas.haulmont.com/cuba/screen/window.xsd"
        xmlns:app="http://schemas.company.com/demo/0.1/ui-component.xsd" (1)
        <instance id="fooDc" class="com.company.demo.entity.Foo" view="_local">
        <form id="form" dataContainer="fooDc">
            <column width="250px">
                <textField id="nameField" property="name"/>
                <app:stepperField id="ageField" property="limit" step="10"/> (2)
1 - the namespace referencing the component’s XSD.
2 - the composite component connected to the limit attribute of an entity.
Custom styling

Now let’s apply some custom styles to improve the component look.

First, change the root component to CssLayout and assign style names to the inner components. Besides custom styles defined in the project (see below), the following predefined styles are used: v-component-group, icon-only.

<composite xmlns="http://schemas.haulmont.com/cuba/screen/composite.xsd">
    <cssLayout id="rootBox" width="100%" stylename="v-component-group stepper-field">
        <textField id="valueField"/>
        <button id="upBtn"
                stylename="stepper-btn icon-only"/>
        <button id="downBtn"
                stylename="stepper-btn icon-only"/>

Change the component class accordingly:

public class StepperField
        extends CompositeComponent<CssLayout>
        implements ...

Generate theme extension (see here how to do it in Studio) and add the following code to the modules/web/themes/hover/com.company.demo/hover-ext.scss file:

@mixin com_company_demo-hover-ext {

  .stepper-field {
    display: flex;

    .stepper-btn {
      width: $v-unit-size;
      min-width: $v-unit-size;

Restart the application server and open the screen. The form with our composite Stepper component should look as follows:

stepper final