mapreduce/src/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;
}