001// Copyright 2006, 2007, 2008, 2013 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.services;
016
017import org.apache.tapestry5.Asset;
018import org.apache.tapestry5.ioc.Resource;
019
020/**
021 * Used by {@link AssetSource} to create new {@link Asset}s as needed.
022 * <p/>
023 * Starting in Tapestry 5.4, the built-in implementations of this interface (for context assets, and for classpath assets)
024 * were changed so that when underlying resources changed, the client URLs for Assets are discarded; this is necessitated by two factors:
025 * <p/>1) the {@linkplain org.apache.tapestry5.Asset#toClientURL() client URL}
026 * for an Asset now includes a checksum based on the content of the underlying resource, so a change to resource content
027 * (during development) results in a change to the URL.
028 * <p/>2) {@link org.apache.tapestry5.services.javascript.JavaScriptStack} (especially the {@link org.apache.tapestry5.services.javascript.ExtensibleJavaScriptStack} implementation)
029 * made no provision for rebuilding the Assets post-construction, and there is no backwards compatible way to
030 * introduce this concept (and JavaScriptStacks are something many applications and third-party libraries make use of).
031 * <p/>So, starting in Tapestry 5.4, the implementations of {@link Asset} should be
032 *
033 * @see org.apache.tapestry5.services.AssetSource
034 */
035public interface AssetFactory
036{
037    /**
038     * Returns the Resource representing the root folder of the domain this factory is responsible for.
039     */
040    Resource getRootResource();
041
042    /**
043     * Creates an instance of an asset. Starting with 5.1.0.0, it is preferred (but not required) that the factory
044     * return an instance of {@link org.apache.tapestry5.Asset2}.
045     *
046     * @param resource
047     *         a resource within this factories domain (derived from the {@linkplain #getRootResource() root
048     *         resource})
049     * @return an Asset for the resource
050     */
051    Asset createAsset(Resource resource);
052}