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 }