/*
* 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 gobblin.source.extractor.hadoop;
import java.io.IOException;
import org.apache.hadoop.mapred.RecordReader;
import gobblin.source.extractor.DataRecordException;
import gobblin.source.extractor.Extractor;
/**
* An implementation of {@link Extractor} that uses a Hadoop {@link RecordReader} to read records
* from a {@link org.apache.hadoop.mapred.FileSplit}.
*
* <p>
* This class is equivalent to {@link HadoopFileInputExtractor} in terms of functionality except that
* it uses the old Hadoop API.
* </p>
*
* <p>
* This class can read either keys of type {@link #<K>} or values of type {@link #<V>} using the
* given {@link RecordReader}, depending on the value of the second argument of the constructor
* {@link #OldApiHadoopFileInputExtractor(RecordReader, boolean)}. It will read keys if the argument
* is {@code true}, otherwise it will read values. Normally, this is specified using the property
* {@link HadoopFileInputSource#FILE_INPUT_READ_KEYS_KEY}, which is {@code false} by default.
* </p>
*
* <p>
* This class provides a default implementation of {@link #readRecord(Object)} that simply casts
* the keys or values read by the {@link RecordReader} into type {@link #<D>}. It is required
* that type {@link #<K>} or {@link #<V>} can be safely casted to type {@link #<D>}.
* </p>
*
* <p>
* The Hadoop {@link RecordReader} is passed into this class, which is responsible for closing
* it by calling {@link RecordReader#close()} in {@link #close()}.
* </p>
*
* <p>
* A concrete implementation of this class should at least implement the {@link #getSchema()}
* method.
* </p>
*
* @param <S> output schema type
* @param <D> output data record type that MUST be compatible with either {@link #<K>} or {@link #<V>}
* @param <K> key type expected by the {@link RecordReader}
* @param <V> value type expected by the {@link RecordReader}
*
* @author Yinan Li
*/
public abstract class OldApiHadoopFileInputExtractor<S, D, K, V> implements Extractor<S, D> {
private final RecordReader<K, V> recordReader;
private final boolean readKeys;
public OldApiHadoopFileInputExtractor(RecordReader<K, V> recordReader, boolean readKeys) {
this.recordReader = recordReader;
this.readKeys = readKeys;
}
/**
* {@inheritDoc}.
*
* This method will throw a {@link ClassCastException} if type {@link #<D>} is not compatible
* with type {@link #<K>} if keys are supposed to be read, or if it is not compatible with type
* {@link #<V>} if values are supposed to be read.
*/
@Override
@SuppressWarnings("unchecked")
public D readRecord(@Deprecated D reuse) throws DataRecordException, IOException {
K key = this.recordReader.createKey();
V value = this.recordReader.createValue();
if (this.recordReader.next(key, value)) {
return this.readKeys ? (D) key : (D) value;
}
return null;
}
@Override
public long getExpectedRecordCount() {
return -1l;
}
@Override
public long getHighWatermark() {
return -1l;
}
@Override
public void close() throws IOException {
this.recordReader.close();
}
}