001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce;
020
021import java.io.IOException;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * A context object that allows input and output from the task. It is only
028 * supplied to the {@link Mapper} or {@link Reducer}.
029 * @param <KEYIN> the input key type for the task
030 * @param <VALUEIN> the input value type for the task
031 * @param <KEYOUT> the output key type for the task
032 * @param <VALUEOUT> the output value type for the task
033 */
034@InterfaceAudience.Public
035@InterfaceStability.Evolving
036public interface TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT> 
037       extends TaskAttemptContext {
038
039  /**
040   * Advance to the next key, value pair, returning null if at end.
041   * @return the key object that was read into, or null if no more
042   */
043  public boolean nextKeyValue() throws IOException, InterruptedException;
044 
045  /**
046   * Get the current key.
047   * @return the current key object or null if there isn't one
048   * @throws IOException
049   * @throws InterruptedException
050   */
051  public KEYIN getCurrentKey() throws IOException, InterruptedException;
052
053  /**
054   * Get the current value.
055   * @return the value object that was read into
056   * @throws IOException
057   * @throws InterruptedException
058   */
059  public VALUEIN getCurrentValue() throws IOException, InterruptedException;
060
061  /**
062   * Generate an output key/value pair.
063   */
064  public void write(KEYOUT key, VALUEOUT value) 
065      throws IOException, InterruptedException;
066
067  /**
068   * Get the {@link OutputCommitter} for the task-attempt.
069   * @return the <code>OutputCommitter</code> for the task-attempt
070   */
071  public OutputCommitter getOutputCommitter();
072}