2005-12-08 07:13:07 +00:00

180 lines
5.8 KiB
Java

/*
* Copyright (C) 2005 Jesper Steen Møller
*
* Licensed under the Mozilla Public License version 1.1
* with a permitted attribution clause. You may obtain a
* copy of the License at
*
* http://www.alfresco.org/legal/license.txt
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
* either express or implied. See the License for the specific
* language governing permissions and limitations under the
* License.
*/
package org.alfresco.repo.content.metadata;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.alfresco.error.AlfrescoRuntimeException;
import org.alfresco.repo.content.MimetypeMap;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.Assert;
/**
* Holds and provides the most appropriate metadate extracter for a particular
* mimetype.
* <p>
* The extracters themselves know how well they are able to extract metadata.
*
* @see org.alfresco.repo.content.metadata.MetadataExtracter
* @author Jesper Steen Møller
*/
public class MetadataExtracterRegistry
{
private static final Log logger = LogFactory.getLog(MetadataExtracterRegistry.class);
private List<MetadataExtracter> extracters;
private Map<String, MetadataExtracter> extracterCache;
private MimetypeMap mimetypeMap;
/** Controls read access to the cache */
private Lock extracterCacheReadLock;
/** controls write access to the cache */
private Lock extracterCacheWriteLock;
/**
* @param mimetypeMap all the mimetypes available to the system
*/
public MetadataExtracterRegistry(MimetypeMap mimetypeMap)
{
Assert.notNull(mimetypeMap, "The MimetypeMap is mandatory");
this.mimetypeMap = mimetypeMap;
extracters = Collections.emptyList(); // just in case it isn't set
extracterCache = new HashMap<String, MetadataExtracter>(17);
// create lock objects for access to the cache
ReadWriteLock extractionCacheLock = new ReentrantReadWriteLock();
extracterCacheReadLock = extractionCacheLock.readLock();
extracterCacheWriteLock = extractionCacheLock.writeLock();
}
/**
* Gets the best metadata extracter. This is a combination of the most
* reliable and the most performant extracter.
* <p>
* The result is cached for quicker access next time.
*
* @param mimetype the source MIME of the extraction
* @return Returns a metadata extracter that can extract metadata from the
* chosen MIME type.
*/
public MetadataExtracter getExtracter(String sourceMimetype)
{
// check that the mimetypes are valid
if (!mimetypeMap.getMimetypes().contains(sourceMimetype))
{
throw new AlfrescoRuntimeException("Unknown extraction source mimetype: " + sourceMimetype);
}
MetadataExtracter extracter = null;
extracterCacheReadLock.lock();
try
{
if (extracterCache.containsKey(sourceMimetype))
{
// the translation has been requested before
// it might have been null
return extracterCache.get(sourceMimetype);
}
}
finally
{
extracterCacheReadLock.unlock();
}
// the translation has not been requested before
// get a write lock on the cache
// no double check done as it is not an expensive task
extracterCacheWriteLock.lock();
try
{
// find the most suitable transformer - may be empty list
extracter = findBestExtracter(sourceMimetype);
// store the result even if it is null
extracterCache.put(sourceMimetype, extracter);
return extracter;
}
finally
{
extracterCacheWriteLock.unlock();
}
}
/**
* @param sourceMimetype The MIME type under examination
* @return The fastest of the most reliable extracters in
* <code>extracters</code> for the given MIME type.
*/
private MetadataExtracter findBestExtracter(String sourceMimetype)
{
double bestReliability = -1;
long bestTime = Long.MAX_VALUE;
logger.debug("Finding best extracter for " + sourceMimetype);
MetadataExtracter bestExtracter = null;
for (MetadataExtracter ext : extracters)
{
double r = ext.getReliability(sourceMimetype);
if (r == bestReliability)
{
long time = ext.getExtractionTime();
if (time < bestTime)
{
bestExtracter = ext;
bestTime = time;
}
}
else if (r > bestReliability)
{
bestExtracter = ext;
bestReliability = r;
bestTime = ext.getExtractionTime();
}
}
return bestExtracter;
}
/**
* Provides a list of self-discovering extracters.
*
* @param transformers all the available extracters that the registry can
* work with
*/
public void setExtracters(List<MetadataExtracter> extracters)
{
logger.debug("Setting " + extracters.size() + "new extracters.");
extracterCacheWriteLock.lock();
try
{
this.extracters = extracters;
this.extracterCache.clear();
}
finally
{
extracterCacheWriteLock.unlock();
}
}
}