001    // Copyright 2005 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.tapestry.asset;
016    
017    /**
018     * Calculates the digest value, as a string, for a particular classpath resource. This is primarily
019     * used by the {@link org.apache.tapestry.asset.AssetService}to authenticate requests (you are not
020     * allowed access to a resource unless you can provide the correct digest value).
021     * 
022     * @author Howard M. Lewis Ship
023     * @since 4.0
024     */
025    public interface ResourceDigestSource
026    {
027        /**
028         * Calculates the DIGEST checksum for a classpath resource. Because this is expensive, the value
029         * may be cached.
030         * 
031         * @param resourcePath
032         *            the classpath resource, which should start with a leading slash.
033         * @return A string representation of the digest for the provided resource path.
034         * @throws ApplicationRuntimeException
035         *             if the resource does not exist, or there is an error calculating the checksum.
036         */
037    
038        public String getDigestForResource(String resourcePath);
039    }