001// Copyright 2006, 2008, 2009, 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; 016 017import org.apache.tapestry5.ioc.Resource; 018 019/** 020 * An Asset is any kind of resource that can be exposed to the client web browser. Although quite often an Asset is a 021 * resource in a web application's context folder, within Tapestry, Assets may also be resources on the classpath (i.e., 022 * packaged inside JARs). 023 * <p/> 024 * An Asset's toString() will return the URL for the resource (the same value as {@link #toClientURL()}). 025 * <p/> 026 * Release 5.1.0.0 introduced {@link org.apache.tapestry5.Asset2}, which extends this interface with an additional 027 * method. 028 * 029 * @see org.apache.tapestry5.services.AssetPathConverter 030 */ 031public interface Asset 032{ 033 /** 034 * Returns a URL that can be passed, unchanged, to the client in order for it to access the resource. The same value 035 * is returned from <code>toString()</code>. 036 * <p/> 037 * Tapestry's built-in asset types (context and classpath) always incorporate a checksum as part of the path, 038 * and alternate implementations are encouraged to do so as well. In addition, Tapestry ensures that context and 039 * classpath assets have a far-future expires header (to ensure aggressive caching by the client). 040 * <p/>Note that starting in Tapestry 5.4, it is expected that Asset instances recognize 041 * when the underlying Resource's content has changed, and update the clientURL to reflect the new content's 042 * checksum. This wasn't an issue in earlier releases where the clientURL incorporated a version number. 043 * <p/> 044 * Finally, starting in 5.4, this value will often be <em>variant</em>: the exact URL returned will depend on 045 * whether the underlying resource content is compressable, whether the current {@link org.apache.tapestry5.services.Request} 046 * supports compression. 047 * 048 * @see org.apache.tapestry5.services.AssetSource 049 * @see org.apache.tapestry5.services.AssetPathConverter 050 */ 051 String toClientURL(); 052 053 /** 054 * Returns the underlying Resource for the Asset. 055 */ 056 Resource getResource(); 057 058}