001// Copyright 2011, 2012 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.assets;
016
017import org.apache.tapestry5.commons.Resource;
018import org.apache.tapestry5.commons.services.InvalidationEventHub;
019import org.apache.tapestry5.commons.services.InvalidationListener;
020import org.apache.tapestry5.ioc.internal.util.URLChangeTracker;
021import org.apache.tapestry5.ioc.services.UpdateListener;
022import org.apache.tapestry5.services.assets.ResourceDependencies;
023
024/**
025 * Tracks resources (at least, resources that can change because they are on the file system) and
026 * acts as an {@link UpdateListener} to check for changes and notify its listeners.
027 *
028 * @since 5.3
029 */
030public interface ResourceChangeTracker extends InvalidationEventHub, ResourceDependencies
031{
032    /**
033     * Start tracking the resource (or return the last modified time of an already tracked resource). Only file system
034     * resources are tracked. Resources are tracked until <em>any</em> resource changes, at which points
035     * {@linkplain InvalidationListener listeners} are notified and the internal state
036     * is cleared.
037     *
038     * @param resource
039     *         to track
040     * @return last modified time, to nearest second
041     * @see URLChangeTracker
042     */
043    long trackResource(Resource resource);
044
045    /**
046     * Forces an invalidation event. This is required in a rare case, to clear out a {@link org.apache.tapestry5.services.assets.StreamableResource}
047     * generated from the component message catalog; there are some walls in place that prevent the message catalog's underlying
048     * {@link Resource}s from being exposed.
049     *
050     * @see org.apache.tapestry5.internal.util.MessageCatalogResource
051     * @since 5.4
052     */
053    void forceInvalidationEvent();
054}