org.apache.mahout.common.iterator.sequencefile.SequenceFileValueIterator Maven / Gradle / Ivy
/**
* 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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* {@link java.util.Iterator} over a {@link SequenceFile}'s values only.
*/
public final class SequenceFileValueIterator extends AbstractIterator implements Closeable {
private final SequenceFile.Reader reader;
private final Configuration conf;
private final Class valueClass;
private final Writable key;
private V value;
private final boolean reuseKeyValueInstances;
private static final Logger log = LoggerFactory.getLogger(SequenceFileValueIterator.class);
/**
* @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 = fs.makeQualified(path);
reader = new SequenceFile.Reader(fs, path, conf);
this.conf = conf;
Class keyClass = (Class) reader.getKeyClass();
key = ReflectionUtils.newInstance(keyClass, conf);
valueClass = (Class) reader.getValueClass();
this.reuseKeyValueInstances = reuseKeyValueInstances;
}
public Class getValueClass() {
return valueClass;
}
@Override
public void close() throws IOException {
value = null;
Closeables.close(reader, true);
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) {
try {
close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
throw new IllegalStateException(ioe);
}
}
}