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    import org.apache.hivemind.ApplicationRuntimeException;
018    
019    /**
020     * Calculates the digest value, as a string, for a particular classpath resource. This is primarily
021     * used by the {@link org.apache.tapestry.asset.AssetService}to authenticate requests (you are not
022     * allowed access to a resource unless you can provide the correct digest value).
023     * 
024     * @author Howard M. Lewis Ship
025     * @since 4.0
026     */
027    public interface ResourceDigestSource
028    {
029        /**
030         * Calculates the DIGEST checksum for a classpath resource. Because this is expensive, the value
031         * may be cached.
032         * 
033         * @param resourcePath
034         *            the classpath resource, which should start with a leading slash.
035         * @return A string representation of the digest for the provided resource path.
036         * @throws ApplicationRuntimeException
037         *             if the resource does not exist, or there is an error calculating the checksum.
038         */
039    
040        String getDigestForResource(String resourcePath);
041    }