    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;
    014
    015/**
    016 * Converts the {@linkplain org.apache.tapestry5.Asset#toClientURL() path (or URI) of an asset} into a new format. This
    017 * is the <em>hook</em> needed to make use of a <a href="http://en.wikipedia.org/wiki/Content_Delivery_Network">Content
    018 * Delivery Network</a>.
    019 *
    020 * The default implementation of this is <em>identity</em>, the URI is passed through unchanged. Using a contribution to
    021 * the {@link org.apache.tapestry5.ioc.services.ServiceOverride} service, you may override the default implementation.
    022 *
    023 * @since 5.1.0.0
    024 */
    025public interface AssetPathConverter
    026{
    027    /**
    028     * Returns true if the converter returns the exact same converted path for any specific asset path (in which case, the
    029     * converted asset path may be cached in component instance variables more aggressively). This value should be false
    030     * if the converted path can vary for the same input path ... that is, if external factors (such as the identity of
    031     * the user, or information obtained from the request) is involved in generating the final client URI. With a CDN
    032     * this can sometimes be the case, where the user's identity may indicate which CDN server to vend the asset from.
    033     *
    034     * @return true if invariant (and therefore cacheable)
    035     */
    036    boolean isInvariant();
    037
    038    /**
    039     * Converts the default asset client URI to its final form, ready to be sent to the client. The default asset path
    040     * is an absolute path (it starts with a leading slash) and incorporates the context path if any.
    041     *
    042     * @param assetPath default asset path
    043     * @return a URI that can be sent to the client
    044     */
    045    String convertAssetPath(String assetPath);
    046}