hadoop ReduceContext 源码
haddop ReduceContext 代码
文件路径：/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/ReduceContext.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.mapreduce;
import java.io.IOException;
import java.util.Iterator;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* The context passed to the {@link Reducer}.
* @param <KEYIN> the class of the input keys
* @param <VALUEIN> the class of the input values
* @param <KEYOUT> the class of the output keys
* @param <VALUEOUT> the class of the output values
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
extends TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT> {
/** Start processing next unique key. */
public boolean nextKey() throws IOException,InterruptedException;
/**
* Iterate through the values for the current key, reusing the same value
* object, which is stored in the context.
* @return the series of values associated with the current key. All of the
* objects returned directly and indirectly from this method are reused.
*/
public Iterable<VALUEIN> getValues() throws IOException, InterruptedException;
/**
* {@link Iterator} to iterate over values for a given group of records.
*/
interface ValueIterator<VALUEIN> extends MarkableIteratorInterface<VALUEIN> {
/**
* This method is called when the reducer moves from one key to
* another.
* @throws IOException
*/
void resetBackupStore() throws IOException;
}
}
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