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.services.assets;
014
015import org.apache.tapestry5.Asset;
016import org.apache.tapestry5.internal.services.AssetDispatcher;
017import org.apache.tapestry5.services.Request;
018import org.apache.tapestry5.services.Response;
019
020import javax.servlet.http.HttpServletResponse;
021import java.io.IOException;
022
023/**
024 * Handler for asset requests, which expose some kind of {@link Asset} to
025 * the user agent (i.e., the client web browser). When contributed to the {@link AssetDispatcher} service,
026 * the contributed key is a handler id (such as "meta/core").
027 * <p/>
028 * An example request path might be <code>/assets/meta/core/dd8d73ac51dbab28caaec4865d302bf2/deselect.png</code>.
029 * The handler id would be
030 * <code>meta/core</code>, the {@linkplain AssetChecksumGenerator checksum of the resource content} is the
031 * hex string, and the extra path would be <code>select.png</code>.
032 *
033 * @see AssetDispatcher
034 * @see org.apache.tapestry5.services.AssetRequestDispatcher
035 * @see AssetPathConstructor
036 * @since 5.2.0
037 */
038public interface AssetRequestHandler
039{
040    /**
041     * Given a request targeted (via the handler id) to the specific handler, process the request.
042     * The handler is responsible for processing the request, sending back either a bytestream
043     * (via {@link Response#getOutputStream(String)}) or an error response
044     * (via {@link Response#sendError(int, String)}). It is the handler's responsibility to allow
045     * for client-side caching (possibly sending an {@link HttpServletResponse#SC_NOT_MODIFIED} response).
046     * <p/>
047     * The handler should return true if it provided a response. If the handler returns false, this indicates that the
048     * extra path did not identify a known asset (virtual or otherwise) and the AssetDispatcher service should send a
049     * {@link HttpServletResponse#SC_NOT_FOUND} response.
050     * <p/>
051     * Starting in Tapestry 5.4, the handler is informed by the {@link org.apache.tapestry5.services.AssetRequestDispatcher}
052     * whether or not the content should be compressed (this is determined based on information in the URL).
053     *
054     * @param request
055     *         incoming asset request
056     * @param response
057     *         used to send a response to client
058     * @param extraPath
059     *         additional path to identify the specific asset
060     * @return true if request was handled (and response sent), false if asset not found
061     */
062    boolean handleAssetRequest(Request request, Response response, String extraPath) throws IOException;
063}