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.lib.join;
020    
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.io.Writable;
026    import org.apache.hadoop.io.WritableComparable;
027    import org.apache.hadoop.mapreduce.RecordReader;
028    
029    /**
030     * Additional operations required of a RecordReader to participate in a join.
031     */
032    @InterfaceAudience.Public
033    @InterfaceStability.Stable
034    public abstract class ComposableRecordReader<K extends WritableComparable<?>,
035                                                 V extends Writable>
036        extends RecordReader<K,V>
037        implements Comparable<ComposableRecordReader<K,?>> {
038    
039      /**
040       * Return the position in the collector this class occupies.
041       */
042      abstract int id();
043    
044      /**
045       * Return the key this RecordReader would supply on a call to next(K,V)
046       */
047      abstract K key();
048    
049      /**
050       * Clone the key at the head of this RecordReader into the object provided.
051       */
052      abstract void key(K key) throws IOException;
053    
054      /**
055       * Create instance of key.
056       */
057      abstract K createKey();
058      
059      /**
060       * Create instance of value.
061       */
062      abstract V createValue();
063      
064      /**
065       * Returns true if the stream is not empty, but provides no guarantee that
066       * a call to next(K,V) will succeed.
067       */
068      abstract boolean hasNext();
069    
070      /**
071       * Skip key-value pairs with keys less than or equal to the key provided.
072       */
073      abstract void skip(K key) throws IOException, InterruptedException;
074    
075      /**
076       * While key-value pairs from this RecordReader match the given key, register
077       * them with the JoinCollector provided.
078       */
079      @SuppressWarnings("unchecked")
080      abstract void accept(CompositeRecordReader.JoinCollector jc, K key) 
081          throws IOException, InterruptedException;
082    }