/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.apache.mahout.cf.taste.impl.similarity.file;
import java.io.File;
import java.util.Collection;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.similarity.GenericItemSimilarity;
import org.apache.mahout.cf.taste.similarity.ItemSimilarity;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.google.common.base.Preconditions;
/**
* <p>
* An {@link ItemSimilarity} backed by a comma-delimited file. This class typically expects a file where each line
* contains an item ID, followed by another item ID, followed by a similarity value, separated by commas. You may also
* use tabs.
* </p>
*
* <p>
* The similarity value is assumed to be parseable as a {@code double} having a value between -1 and 1. The
* item IDs are parsed as {@code long}s. Similarities are symmetric so for a pair of items you do not have to
* include 2 lines in the file.
* </p>
*
* <p>
* This class will reload data from the data file when {@link #refresh(Collection)} is called, unless the file
* has been reloaded very recently already.
* </p>
*
* <p>
* This class is not intended for use with very large amounts of data. For that, a JDBC-backed {@link ItemSimilarity}
* and a database are more appropriate.
* </p>
*/
public class FileItemSimilarity implements ItemSimilarity {
public static final long DEFAULT_MIN_RELOAD_INTERVAL_MS = 60 * 1000L; // 1 minute?
private ItemSimilarity delegate;
private final ReentrantLock reloadLock;
private final File dataFile;
private long lastModified;
private final long minReloadIntervalMS;
private static final Logger log = LoggerFactory.getLogger(FileItemSimilarity.class);
/**
* @param dataFile
* file containing the similarity data
*/
public FileItemSimilarity(File dataFile) {
this(dataFile, DEFAULT_MIN_RELOAD_INTERVAL_MS);
}
/**
* @param minReloadIntervalMS
* the minimum interval in milliseconds after which a full reload of the original datafile is done
* when refresh() is called
* @see #FileItemSimilarity(File)
*/
public FileItemSimilarity(File dataFile, long minReloadIntervalMS) {
Preconditions.checkArgument(dataFile != null, "dataFile is null");
Preconditions.checkArgument(dataFile.exists() && !dataFile.isDirectory(),
"dataFile is missing or a directory: %s", dataFile);
log.info("Creating FileItemSimilarity for file {}", dataFile);
this.dataFile = dataFile.getAbsoluteFile();
this.lastModified = dataFile.lastModified();
this.minReloadIntervalMS = minReloadIntervalMS;
this.reloadLock = new ReentrantLock();
reload();
}
@Override
public double[] itemSimilarities(long itemID1, long[] itemID2s) throws TasteException {
return delegate.itemSimilarities(itemID1, itemID2s);
}
@Override
public long[] allSimilarItemIDs(long itemID) throws TasteException {
return delegate.allSimilarItemIDs(itemID);
}
@Override
public double itemSimilarity(long itemID1, long itemID2) throws TasteException {
return delegate.itemSimilarity(itemID1, itemID2);
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
if (dataFile.lastModified() > lastModified + minReloadIntervalMS) {
log.debug("File has changed; reloading...");
reload();
}
}
protected void reload() {
if (reloadLock.tryLock()) {
try {
long newLastModified = dataFile.lastModified();
delegate = new GenericItemSimilarity(new FileItemItemSimilarityIterable(dataFile));
lastModified = newLastModified;
} finally {
reloadLock.unlock();
}
}
}
@Override
public String toString() {
return "FileItemSimilarity[dataFile:" + dataFile + ']';
}
}