    001    // Copyright 2011 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.internal.services.assets;
    016
    017    import org.apache.tapestry5.internal.TapestryInternalUtils;
    018    import org.apache.tapestry5.ioc.Resource;
    019    import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
    020    import org.apache.tapestry5.services.InvalidationListener;
    021    import org.apache.tapestry5.services.assets.ResourceDependencies;
    022    import org.apache.tapestry5.services.assets.StreamableResource;
    023    import org.apache.tapestry5.services.assets.StreamableResourceProcessing;
    024    import org.apache.tapestry5.services.assets.StreamableResourceSource;
    025
    026    import java.io.IOException;
    027    import java.lang.ref.SoftReference;
    028    import java.util.Map;
    029
    030    /**
    031     * An interceptor for the {@link StreamableResourceSource} service that handles caching of content.
    032     */
    033    public class SRSCachingInterceptor implements StreamableResourceSource, InvalidationListener
    034    {
    035        private final StreamableResourceSource delegate;
    036
    037        private final Map<Resource, SoftReference<StreamableResource>> cache = CollectionFactory.newConcurrentMap();
    038
    039        public SRSCachingInterceptor(StreamableResourceSource delegate)
    040        {
    041            this.delegate = delegate;
    042        }
    043
    044        public StreamableResource getStreamableResource(Resource baseResource, StreamableResourceProcessing processing, ResourceDependencies dependencies)
    045                throws IOException
    046        {
    047            if (!enableCache(processing))
    048            {
    049                return delegate.getStreamableResource(baseResource, processing, dependencies);
    050            }
    051
    052            StreamableResource result = TapestryInternalUtils.getAndDeref(cache, baseResource);
    053
    054            if (result == null)
    055            {
    056                result = delegate.getStreamableResource(baseResource, processing, dependencies);
    057
    058                if (isCacheable(result))
    059                {
    060                    dependencies.addDependency(baseResource);
    061
    062                    cache.put(baseResource, new SoftReference<StreamableResource>(result));
    063                }
    064            }
    065
    066            return result;
    067        }
    068
    069        /**
    070         * Always returns true; a subclass may extend this to only cache the resource in some circumstances.
    071         *
    072         * @param resource
    073         * @return true to cache the resource
    074         */
    075        protected boolean isCacheable(StreamableResource resource)
    076        {
    077            return true;
    078        }
    079
    080        public void objectWasInvalidated()
    081        {
    082            cache.clear();
    083        }
    084
    085        /**
    086         * Returns true unless the processing is {@link StreamableResourceProcessing#FOR_AGGREGATION}.
    087         * Subclasses may override. When the cache is not enabled, the request is passed on to the interceptor's
    088         * {@link #delegate}, and no attempt is made to read or update this interceptor's cache.
    089         *
    090         * @since 5.3.5
    091         */
    092        protected boolean enableCache(StreamableResourceProcessing processing)
    093        {
    094            return processing != StreamableResourceProcessing.FOR_AGGREGATION;
    095        }
    096    }