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
015package org.apache.tapestry5.internal.services.assets;
016
017import org.apache.tapestry5.internal.TapestryInternalUtils;
018import org.apache.tapestry5.ioc.Resource;
019import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
020import org.apache.tapestry5.services.InvalidationListener;
021import org.apache.tapestry5.services.assets.ResourceDependencies;
022import org.apache.tapestry5.services.assets.StreamableResource;
023import org.apache.tapestry5.services.assets.StreamableResourceProcessing;
024import org.apache.tapestry5.services.assets.StreamableResourceSource;
025
026import java.io.IOException;
027import java.lang.ref.SoftReference;
028import java.util.Map;
029
030/**
031 * An interceptor for the {@link StreamableResourceSource} service that handles caching of content.
032 */
033public 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}