    001// Copyright 2011, 2012 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.commons.Resource;
    018import org.apache.tapestry5.commons.util.CollectionFactory;
    019import org.apache.tapestry5.internal.TapestryInternalUtils;
    020import org.apache.tapestry5.services.assets.ResourceDependencies;
    021import org.apache.tapestry5.services.assets.StreamableResource;
    022import org.apache.tapestry5.services.assets.StreamableResourceProcessing;
    023import org.apache.tapestry5.services.assets.StreamableResourceSource;
    024
    025import java.io.IOException;
    026import java.lang.ref.SoftReference;
    027import java.util.Map;
    028
    029/**
    030 * An interceptor for the {@link StreamableResourceSource} service that handles caching of content.
    031 */
    032public class SRSCachingInterceptor extends DelegatingSRS
    033{
    034    private final Map<Resource, SoftReference<StreamableResource>> cache = CollectionFactory.newConcurrentMap();
    035
    036    public SRSCachingInterceptor(StreamableResourceSource delegate, ResourceChangeTracker tracker)
    037    {
    038        super(delegate);
    039
    040        tracker.clearOnInvalidation(cache);
    041    }
    042
    043    public StreamableResource getStreamableResource(Resource baseResource, StreamableResourceProcessing processing, ResourceDependencies dependencies)
    044            throws IOException
    045    {
    046        if (!enableCache(processing))
    047        {
    048            return delegate.getStreamableResource(baseResource, processing, dependencies);
    049        }
    050
    051        StreamableResource result = TapestryInternalUtils.getAndDeref(cache, baseResource);
    052
    053        if (result == null)
    054        {
    055            result = delegate.getStreamableResource(baseResource, processing, dependencies);
    056
    057            if (isCacheable(result))
    058            {
    059                dependencies.addDependency(baseResource);
    060
    061                cache.put(baseResource, new SoftReference<StreamableResource>(result));
    062            }
    063        }
    064
    065        return result;
    066    }
    067
    068    /**
    069     * Always returns true; a subclass may extend this to only cache the resource in some circumstances.
    070     *
    071     * @param resource
    072     * @return true to cache the resource
    073     */
    074    protected boolean isCacheable(StreamableResource resource)
    075    {
    076        return true;
    077    }
    078
    079    /**
    080     * Returns true unless the processing is {@link StreamableResourceProcessing#FOR_AGGREGATION}.
    081     * Subclasses may override. When the cache is not enabled, the request is passed on to the interceptor's
    082     * {@link #delegate}, and no attempt is made to read or update this interceptor's cache.
    083     *
    084     * @since 5.3.5
    085     */
    086    protected boolean enableCache(StreamableResourceProcessing processing)
    087    {
    088        return processing != StreamableResourceProcessing.FOR_AGGREGATION;
    089    }
    090}