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    
019    package org.apache.hadoop.mapreduce;
020    
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import 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
036    public 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    }