    001    // Copyright 2010 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
    015    package org.apache.tapestry5.services.assets;
    016
    017    import java.io.IOException;
    018
    019    import javax.servlet.http.HttpServletResponse;
    020
    021    import org.apache.tapestry5.Asset;
    022    import org.apache.tapestry5.SymbolConstants;
    023    import org.apache.tapestry5.internal.services.AssetDispatcher;
    024    import org.apache.tapestry5.services.Request;
    025    import org.apache.tapestry5.services.Response;
    026
    027    /**
    028     * Handler for asset requests, which expose some kind of {@link Asset} to
    029     * the user agent (i.e., the client web browser). Starting in Tapestry 5.2,
    030     * asset paths are more structured, consisting of four parts:
    031     * <ul>
    032     * <li><code>/assets/</code> -- the root path for all assets
    033     * <li>
    034     * <em>application version</em> -- the application version, as defined by the
    035     * {@link SymbolConstants#APPLICATION_VERSION} symbol
    036     * <li><em>handler id</em> -- a handler for this part of the asset path (defined by contributions to the
    037     * <code>AssetDispatcher</code> service)
    038     * <li><em>extra path</em> -- additional path beyond the handler id, used to identify the specific resource
    039     * </ul>
    040     * <p>
    041     * So, an example path might be <code>/assets/1.0.1/corelib/components/select.png</code>. The handler id would be
    042     * <code>corelib</code>, and the extra path would be <code>components/select.png</code>.
    043     *
    044     * @since 5.2.0
    045     * @see AssetDispatcher
    046     */
    047    public interface AssetRequestHandler
    048    {
    049        /**
    050         * Given a request targeted (via the handler id) to the specific handler, process the request.
    051         * The handler is responsible for processing the request, sending back either a bytestream
    052         * (via {@link Response#getOutputStream(String)}) or an error response
    053         * (via {@link Response#sendError(int, String)}). It is the handler's responsibility to allow
    054         * for client-side caching (possibly sending an {@link HttpServletResponse#SC_NOT_MODIFIED} response).
    055         * <p>
    056         * The handler should return true if it provided a response. If the handler returns false, this indicates that the
    057         * extra path did not identify a known asset (virtual or otherwise) and the AssetDispatcher service should send a
    058         * {@link HttpServletResponse#SC_NOT_FOUND} response.
    059         *
    060         * @param request
    061         *            incoming asset request
    062         * @param response
    063         *            used to send a response to client
    064         * @param extraPath
    065         *            additional path to identify the specific asset
    066         * @return true if request handler, false if asset not found
    067         */
    068        boolean handleAssetRequest(Request request, Response response, String extraPath) throws IOException;
    069    }