jakarta.faces.view.facelets.ComponentHandler Maven / Gradle / Ivy

/*
 * Copyright (c) 1997, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.faces.view.facelets;

import jakarta.faces.component.UIComponent;

/**
 * 
 * Public base class for markup element instances that map to
 * {@link UIComponent} instances in the view.
 * 
 *
 * 
 *
 * 
 * Instances of this class are created and passed to
 * {@link TagHandlerDelegateFactory#createComponentHandlerDelegate} when a tag corresponding to this particular
 * component is encountered in a Facelet view. A custom tag handler for a component, converter, validator, or behavior
 * must extend from this class. In this way, this instance acts as a delegate for the implementation private tag
 * handler. Such a subclass may choose to override as many or as few methods from this base class as desired. If the
 * subclass wants to completely override the action of the implementation specific tag for which this component is the
 * delegate, it must override the apply() method and make it take the following actions, in this
 * order. These actions must only happen the first time this facelet is applied for each user. Subsequent
 * applications must take no action.
 * 
 *
 * 
 *
 * 
 * 
 * The UIComponent represented by this element is created with the appropriate
 * Application.createComponent() method.
 * 
 * 
 *
 * 
 * 
 * Each attribute specified in the markup is correctly applied to the component instance, as specified in the VDLDocs
 * for this element.
 * 
 * 
 *
 * 
 * 
 * If project stage is {@link jakarta.faces.application.ProjectStage#Development}, Put the
 * {@link jakarta.faces.view.Location} for this element into the component attribute Map under the key
 * given by the value of the symbolic constant {@link jakarta.faces.component.UIComponent#VIEW_LOCATION_KEY}.
 * 
 * 
 *
 * 
 * 
 * Set the id of the component. If the id is specified manually by the page author, that value must be set as the id.
 * Otherwise, the closest ancestor component that is an instance of {@link jakarta.faces.component.UniqueIdVendor} must
 * be located and its {@link jakarta.faces.component.UniqueIdVendor#createUniqueId} method must be called to derive the
 * id. If no such instance can be found, call {@link jakarta.faces.component.UIViewRoot#createUniqueId} to derive the
 * id.
 * 
 * 
 *
 * 
 * 
 * The rendererType property of the component is set properly.
 * 
 * 
 *
 * 
 * 
 * {@link #onComponentCreated} is called.
 * 
 * 
 *
 * 
 * 
 * {@link UIComponent#pushComponentToEL} is called on the newly created component.
 * 
 * 
 *
 * 
 * 
 * The next handler in the facelet chain is applied. This will cause the component to be populated with children.
 * 
 * 
 *
 * 
 * 
 * The component is added to its parent in the view.
 * 
 * 
 *
 * 
 * 
 * {@link UIComponent#popComponentFromEL} is called on the newly created component.
 * 
 * 
 *
 * 
 * 
 * Call {@link UIComponent#markInitialState}.
 * 
 * 
 *
 * 
 *
 * 
 *
 * 
 * A common use case for extending this class is to gain access to the process by which the Facelets runtime creates
 * component instances corresponding to markup in a Facelets view. These three methods are useful in such cases.
 * 
 *
 * 
 *
 * 
 * 
 * To control the instantiation of the UIComponent instance, subclasses may override
 * {@link #createComponent}. If this method is not overridden, the tag handler for which this instance is the delegate
 * will take the necessary action to instantiate the UIComponent.
 * 
 * 
 *
 * 
 * 
 * To be notified of creation of the UIComponentinstance, subclasses may override
 * {@link #onComponentCreated}.
 * 
 * 
 *
 * 
 * 
 * To be notified that the freshly created UIComponent instance has been populated with children as a
 * result of execution of child tag handlers, subclasses may override {@link #onComponentPopulated}.
 * 
 * 
 * 
 * 
 *
 * 
 *
 * @since 2.0
 */
public class ComponentHandler extends DelegatingMetaTagHandler {

    private TagHandlerDelegate helper = null;
    private ComponentConfig componentConfig = null;

    /**
     * 
     * Leverage the {@link TagHandlerDelegateFactory} provided by the implementation to create an instance of
     * {@link TagHandlerDelegate} designed for use with ComponentHandler.
     * 
     *
     * @param config the configuration for this handler.
     *
     * @since 2.0
     */
    public ComponentHandler(ComponentConfig config) {
        super(config);
        componentConfig = config;
    }

    @Override
    protected TagHandlerDelegate getTagHandlerDelegate() {
        if (helper == null) {
            helper = delegateFactory.createComponentHandlerDelegate(this);
        }

        return helper;
    }

    /**
     * Returns the component configuration, a component-type/renderer-type pair.
     * @return the component configuration
     */
    public ComponentConfig getComponentConfig() {
        return componentConfig;
    }

    /**
     * 
     * Subclasses that wish to take over the task of instantiating the UIComponent instance corresponding to
     * this tag handler my override this method to do so. A null return from this method will cause the
     * TagHandlerDelegate for instance to create the component instead.
     * 
     *
     * @param ctx the FaceletContext for this view execution
     *
     * @return the newly created {@link UIComponent}
     *
     * @since 2.2
     */
    public UIComponent createComponent(FaceletContext ctx) {
        return null;
    }

    /**
     * 
     * This method is guaranteed to be called after the component has been created but before it has been populated with
     * children.
     * 
     *
     * @param ctx the FaceletContext for this view execution
     *
     * @param c the UIComponent that has just been created.
     *
     * @param parent the parent UIComponent of the component represented by this element instance.
     *
     * @since 2.0
     */
    public void onComponentCreated(FaceletContext ctx, UIComponent c, UIComponent parent) {

    }

    /**
     * 
     * This method is guaranteed to be called after the component has been populated with children.
     * 
     *
     * @param ctx the FaceletContext for this view execution
     *
     * @param c the UIComponent that has just been populated with children.
     *
     * @param parent the parent UIComponent of the component represented by this element instance.
     *
     * @since 2.0
     */
    public void onComponentPopulated(FaceletContext ctx, UIComponent c, UIComponent parent) {

    }

    /**
     * 
     * Determine if the passed component is not null and if it's new to the tree. This operation can be used for determining
     * if attributes should be wired to the component.
     * 
     *
     * @param component the component you wish to modify
     *
     * @return true if and only if the argument is not {@code null} and the component is new during this run of the
     * lifecycle.
     *
     * @since 2.0
     */
    public static boolean isNew(UIComponent component) {
        UIComponent componentToTest = component;
        if (componentToTest == null) {
            return false;
        }

        UIComponent parent = componentToTest.getParent();
        if (parent != null) {
            if (UIComponent.isCompositeComponent(parent)) {
                componentToTest = parent;
            }
        }

        return componentToTest.getParent() == null;
    }

}