hadoop ValueAggregatorMapper 源码
haddop ValueAggregatorMapper 代码
文件路径：/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorMapper.java
/**
* 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.hadoop.mapred.lib.aggregate;
import java.io.IOException;
import java.util.Iterator;
import java.util.Map.Entry;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;
/**
* This class implements the generic mapper of Aggregate.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ValueAggregatorMapper<K1 extends WritableComparable,
V1 extends Writable>
extends ValueAggregatorJobBase<K1, V1> {
/**
* the map function. It iterates through the value aggregator descriptor
* list to generate aggregation id/value pairs and emit them.
*/
public void map(K1 key, V1 value,
OutputCollector<Text, Text> output, Reporter reporter) throws IOException {
Iterator iter = this.aggregatorDescriptorList.iterator();
while (iter.hasNext()) {
ValueAggregatorDescriptor ad = (ValueAggregatorDescriptor) iter.next();
Iterator<Entry<Text, Text>> ens =
ad.generateKeyValPairs(key, value).iterator();
while (ens.hasNext()) {
Entry<Text, Text> en = ens.next();
output.collect(en.getKey(), en.getValue());
}
}
}
/**
* Do nothing. Should not be called.
*/
public void reduce(Text arg0, Iterator<Text> arg1,
OutputCollector<Text, Text> arg2,
Reporter arg3) throws IOException {
throw new IOException("should not be called\n");
}
}
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