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 }