001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005// http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.internal.services;
014
015import org.apache.tapestry5.commons.services.InvalidationEventHub;
016import org.apache.tapestry5.internal.parser.ComponentTemplate;
017import org.apache.tapestry5.model.ComponentModel;
018import org.apache.tapestry5.services.pageload.ComponentResourceSelector;
019
020/**
021 * Provides access to cached {@link org.apache.tapestry5.internal.parser.ComponentTemplate}s. The source acts as a
022 * invalidation event hub, and will broadcast invalidation events when any loaded template resource changes. The
023 * listener for these invalidation events is the page source, which stores cached page instances.
024 *
025 * Any search for a template will end with success (a non-null template), but the template returned may be the
026 * {@link ComponentTemplate#isMissing() missing template}.
027 */
028public interface ComponentTemplateSource
029{
030    /**
031     * Provides access to a template. The template will be parsed as necessary. If no template for the exact component
032     * is found, then the template for the component's parent is returned. In this way, it is possible for a component
033     * to extend the behavior of its super-class without duplicating the super-class component's template.
034     *
035     * In some cases, the empty template will be returned.
036     * 
037     * @param componentModel
038     *            model for the component whose template is to be accessed
039     * @param selector
040     *            defines locale and other information needed to locate template
041     * @return the cached template instance
042     */
043    ComponentTemplate getTemplate(ComponentModel componentModel, ComponentResourceSelector selector);
044
045    /**
046     * Event hub used to notify listeners that underlying component template files have changed.
047     * 
048     * @see org.apache.tapestry5.services.ComponentTemplates
049     * @since 5.1.0.0
050     */
051    InvalidationEventHub getInvalidationEventHub();
052}