001// Copyright 2006, 2008, 2011 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007// http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.internal.services;
016
017import org.apache.tapestry5.internal.parser.ComponentTemplate;
018import org.apache.tapestry5.model.ComponentModel;
019import org.apache.tapestry5.services.InvalidationEventHub;
020import org.apache.tapestry5.services.pageload.ComponentResourceSelector;
021
022/**
023 * Provides access to cached {@link org.apache.tapestry5.internal.parser.ComponentTemplate}s. The source acts as a
024 * invalidation event hub, and will broadcast invalidation events when any loaded template resource changes. The
025 * listener for these invalidation events is the page source, which stores cached page instances.
026 * <p/>
027 * Any search for a template will end with success (a non-null template), but the template returned may be the
028 * {@link ComponentTemplate#isMissing() missing template}.
029 */
030public interface ComponentTemplateSource
031{
032    /**
033     * Provides access to a template. The template will be parsed as necessary. If no template for the exact component
034     * is found, then the template for the component's parent is returned. In this way, it is possible for a component
035     * to extend the behavior of its super-class without duplicating the super-class component's template.
036     * <p/>
037     * In some cases, the empty template will be returned.
038     * 
039     * @param componentModel
040     *            model for the component whose template is to be accessed
041     * @param selector
042     *            defines locale and other information needed to locate template
043     * @return the cached template instance
044     */
045    ComponentTemplate getTemplate(ComponentModel componentModel, ComponentResourceSelector selector);
046
047    /**
048     * Event hub used to notify listeners that underlying component template files have changed.
049     * 
050     * @see org.apache.tapestry5.services.ComponentTemplates
051     * @since 5.1.0.0
052     */
053    InvalidationEventHub getInvalidationEventHub();
054}