hadoop ValueAggregatorReducer 源码
haddop ValueAggregatorReducer 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/ValueAggregatorReducer.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 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 reducer of Aggregate.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ValueAggregatorReducer<K1 extends WritableComparable,
V1 extends Writable>
extends ValueAggregatorJobBase<K1, V1> {
/**
* @param key
* the key is expected to be a Text object, whose prefix indicates
* the type of aggregation to aggregate the values. In effect, data
* driven computing is achieved. It is assumed that each aggregator's
* getReport method emits appropriate output for the aggregator. This
* may be further customiized.
* @param values
* the values to be aggregated
*/
public void reduce(Text key, Iterator<Text> values,
OutputCollector<Text, Text> output, Reporter reporter) throws IOException {
String keyStr = key.toString();
int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR);
String type = keyStr.substring(0, pos);
keyStr = keyStr.substring(pos
+ ValueAggregatorDescriptor.TYPE_SEPARATOR.length());
ValueAggregator aggregator = ValueAggregatorBaseDescriptor
.generateValueAggregator(type);
while (values.hasNext()) {
aggregator.addNextValue(values.next());
}
String val = aggregator.getReport();
key = new Text(keyStr);
output.collect(key, new Text(val));
}
/**
* Do nothing. Should not be called
*/
public void map(K1 arg0, V1 arg1, OutputCollector<Text, Text> arg2,
Reporter arg3) throws IOException {
throw new IOException ("should not be called\n");
}
}
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