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.services.assets;
016
017import org.apache.tapestry5.ioc.Resource;
018
019import java.io.IOException;
020import java.io.InputStream;
021
022/**
023 * A transformer is used to read a {@link Resource} and pass it through a transformation stage, to get a
024 * stream that can be used on the client side. Examples of this are languages that "compile" to
025 * JavaScript, or any of a few higher-level versions of CSS that are compiled to standard CSS.
026 * ResourceTransformers are contributed to the {@link StreamableResourceSource} service.
027 *
028 * @since 5.3
029 * @see StreamableResourceSource
030 */
031public interface ResourceTransformer
032{
033    /**
034     * Returns the MIME type of a transformed stream.
035     *
036     * @since 5.4
037     */
038    String getTransformedContentType();
039
040    /**
041     * Read the source input stream and provide a new input stream of the transformed content.
042     *
043     * @param source
044     *         input content
045     * @param dependencies
046     *         allows additional dependencies of the source to be tracked
047     * @return stream of output content
048     * @throws IOException
049     */
050    InputStream transform(Resource source, ResourceDependencies dependencies) throws IOException;
051}