001// Copyright 2013 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.services.assets.AssetChecksumGenerator;
020import org.apache.tapestry5.services.assets.StreamableResource;
021import org.apache.tapestry5.services.assets.StreamableResourceProcessing;
022import org.apache.tapestry5.services.assets.StreamableResourceSource;
023
024import java.io.IOException;
025import java.io.InputStream;
026import java.util.Map;
027import java.util.zip.Adler32;
028
029public class AssetChecksumGeneratorImpl implements AssetChecksumGenerator
030{
031
032    private final StreamableResourceSource streamableResourceSource;
033
034    private final ResourceChangeTracker tracker;
035
036    private final Map<StreamableResource, String> cache = CollectionFactory.newConcurrentMap();
037
038    public AssetChecksumGeneratorImpl(StreamableResourceSource streamableResourceSource, ResourceChangeTracker tracker)
039    {
040        this.streamableResourceSource = streamableResourceSource;
041        this.tracker = tracker;
042
043        tracker.clearOnInvalidation(cache);
044    }
045
046    public String generateChecksum(Resource resource) throws IOException
047    {
048        StreamableResource streamable = streamableResourceSource.getStreamableResource(resource, StreamableResourceProcessing.COMPRESSION_DISABLED,
049                tracker);
050
051        return generateChecksum(streamable);
052    }
053
054    public String generateChecksum(StreamableResource resource) throws IOException
055    {
056        String result = cache.get(resource);
057
058        if (result == null)
059        {
060            result = toChecksum(resource.openStream());
061
062            cache.put(resource, result);
063        }
064
065        return result;
066    }
067
068    private String toChecksum(InputStream is) throws IOException
069    {
070        // Adler32 is very fast and suitable for these purposes (MD5 and SHA are slower, and
071        // are targetted at cryptographic solutions).
072        Adler32 checksum = new Adler32();
073
074        byte[] buffer = new byte[1024];
075
076        try
077        {
078            while (true)
079            {
080                int length = is.read(buffer);
081
082                if (length < 0)
083                {
084                    break;
085                }
086
087                checksum.update(buffer, 0, length);
088            }
089
090            // Reduces it down to just 32 bits which we express in hex.
091            return Long.toHexString(checksum.getValue());
092        } finally
093        {
094            is.close();
095        }
096    }
097}