hadoop RecordReader 源码
haddop RecordReader 代码
文件路径：/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/RecordReader.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.Closeable;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* The record reader breaks the data into key/value pairs for input to the
* {@link Mapper}.
* @param <KEYIN>
* @param <VALUEIN>
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class RecordReader<KEYIN, VALUEIN> implements Closeable {
/**
* Called once at initialization.
* @param split the split that defines the range of records to read
* @param context the information about the task
* @throws IOException
* @throws InterruptedException
*/
public abstract void initialize(InputSplit split,
TaskAttemptContext context
) throws IOException, InterruptedException;
/**
* Read the next key, value pair.
* @return true if a key/value pair was read
* @throws IOException
* @throws InterruptedException
*/
public abstract
boolean nextKeyValue() throws IOException, InterruptedException;
/**
* Get the current key
* @return the current key or null if there is no current key
* @throws IOException
* @throws InterruptedException
*/
public abstract
KEYIN getCurrentKey() throws IOException, InterruptedException;
/**
* Get the current value.
* @return the object that was read
* @throws IOException
* @throws InterruptedException
*/
public abstract
VALUEIN getCurrentValue() throws IOException, InterruptedException;
/**
* The current progress of the record reader through its data.
* @return a number between 0.0 and 1.0 that is the fraction of the data read
* @throws IOException
* @throws InterruptedException
*/
public abstract float getProgress() throws IOException, InterruptedException;
/**
* Close the record reader.
*/
public abstract void close() throws IOException;
}
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