/**
* 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.common.iterator.sequencefile;
import java.io.Closeable;
import java.io.IOException;
import com.google.common.collect.AbstractIterator;
import com.google.common.io.Closeables;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;
/**
* <p>{@link java.util.Iterator} over a {@link SequenceFile}'s values only.</p>
*/
public final class SequenceFileValueIterator<V extends Writable> extends AbstractIterator<V> implements Closeable {
private final SequenceFile.Reader reader;
private final Configuration conf;
private final Class<V> valueClass;
private final Writable key;
private V value;
private final boolean reuseKeyValueInstances;
/**
* @throws IOException if path can't be read, or its key or value class can't be instantiated
*/
public SequenceFileValueIterator(Path path, boolean reuseKeyValueInstances, Configuration conf) throws IOException {
value = null;
FileSystem fs = path.getFileSystem(conf);
path = path.makeQualified(fs);
reader = new SequenceFile.Reader(fs, path, conf);
this.conf = conf;
Class<? extends Writable> keyClass = (Class<? extends Writable>) reader.getKeyClass();
key = ReflectionUtils.newInstance(keyClass, conf);
valueClass = (Class<V>) reader.getValueClass();
this.reuseKeyValueInstances = reuseKeyValueInstances;
}
public Class<V> getValueClass() {
return valueClass;
}
@Override
public void close() {
value = null;
Closeables.closeQuietly(reader);
endOfData();
}
@Override
protected V computeNext() {
if (!reuseKeyValueInstances || value == null) {
value = ReflectionUtils.newInstance(valueClass, conf);
}
try {
boolean available = reader.next(key, value);
if (!available) {
close();
return null;
}
return value;
} catch (IOException ioe) {
close();
throw new IllegalStateException(ioe);
}
}
}