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.mapred.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.mapred.RecordReader;
028    
029    /**
030     * Additional operations required of a RecordReader to participate in a join.
031     */
032    @InterfaceAudience.Public
033    @InterfaceStability.Stable
034    public interface ComposableRecordReader<K extends WritableComparable,
035                                     V extends Writable>
036        extends RecordReader<K,V>, Comparable<ComposableRecordReader<K,?>> {
037    
038      /**
039       * Return the position in the collector this class occupies.
040       */
041      int id();
042    
043      /**
044       * Return the key this RecordReader would supply on a call to next(K,V)
045       */
046      K key();
047    
048      /**
049       * Clone the key at the head of this RecordReader into the object provided.
050       */
051      void key(K key) throws IOException;
052    
053      /**
054       * Returns true if the stream is not empty, but provides no guarantee that
055       * a call to next(K,V) will succeed.
056       */
057      boolean hasNext();
058    
059      /**
060       * Skip key-value pairs with keys less than or equal to the key provided.
061       */
062      void skip(K key) throws IOException;
063    
064      /**
065       * While key-value pairs from this RecordReader match the given key, register
066       * them with the JoinCollector provided.
067       */
068      void accept(CompositeRecordReader.JoinCollector jc, K key) throws IOException;
069    }