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/mapred/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.mapred;
import java.io.Closeable;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* <code>RecordReader</code> reads <key, value> pairs from an
* {@link InputSplit}.
*
* <p><code>RecordReader</code>, typically, converts the byte-oriented view of
* the input, provided by the <code>InputSplit</code>, and presents a
* record-oriented view for the {@link Mapper} and {@link Reducer} tasks for
* processing. It thus assumes the responsibility of processing record
* boundaries and presenting the tasks with keys and values.</p>
*
* @see InputSplit
* @see InputFormat
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public interface RecordReader<K, V> extends Closeable{
/**
* Reads the next key/value pair from the input for processing.
*
* @param key the key to read data into
* @param value the value to read data into
* @return true iff a key/value was read, false if at EOF
*/
boolean next(K key, V value) throws IOException;
/**
* Create an object of the appropriate type to be used as a key.
*
* @return a new key object.
*/
K createKey();
/**
* Create an object of the appropriate type to be used as a value.
*
* @return a new value object.
*/
V createValue();
/**
* Returns the current position in the input.
*
* @return the current position in the input.
* @throws IOException
*/
long getPos() throws IOException;
/**
* Close this {@link InputSplit} to future operations.
*
* @throws IOException
*/
@Override
public void close() throws IOException;
/**
* How much of the input has the {@link RecordReader} consumed i.e.
* has been processed by?
*
* @return progress from <code>0.0</code> to <code>1.0</code>.
* @throws IOException
*/
float getProgress() throws IOException;
}
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