1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.hadoop.mapred; 20 21 import java.io.IOException; 22 23 import org.apache.hadoop.classification.InterfaceAudience; 24 import org.apache.hadoop.classification.InterfaceStability; 25 26 /** 27 * <code>RecordReader</code> reads <key, value> pairs from an 28 * {@link InputSplit}. 29 * 30 * <p><code>RecordReader</code>, typically, converts the byte-oriented view of 31 * the input, provided by the <code>InputSplit</code>, and presents a 32 * record-oriented view for the {@link Mapper} and {@link Reducer} tasks for 33 * processing. It thus assumes the responsibility of processing record 34 * boundaries and presenting the tasks with keys and values.</p> 35 * 36 * @see InputSplit 37 * @see InputFormat 38 */ 39 @InterfaceAudience.Public 40 @InterfaceStability.Stable 41 public interface RecordReader<K, V> { 42 /** 43 * Reads the next key/value pair from the input for processing. 44 * 45 * @param key the key to read data into 46 * @param value the value to read data into 47 * @return true iff a key/value was read, false if at EOF 48 */ next(K key, V value)49 boolean next(K key, V value) throws IOException; 50 51 /** 52 * Create an object of the appropriate type to be used as a key. 53 * 54 * @return a new key object. 55 */ createKey()56 K createKey(); 57 58 /** 59 * Create an object of the appropriate type to be used as a value. 60 * 61 * @return a new value object. 62 */ createValue()63 V createValue(); 64 65 /** 66 * Returns the current position in the input. 67 * 68 * @return the current position in the input. 69 * @throws IOException 70 */ getPos()71 long getPos() throws IOException; 72 73 /** 74 * Close this {@link InputSplit} to future operations. 75 * 76 * @throws IOException 77 */ close()78 public void close() throws IOException; 79 80 /** 81 * How much of the input has the {@link RecordReader} consumed i.e. 82 * has been processed by? 83 * 84 * @return progress from <code>0.0</code> to <code>1.0</code>. 85 * @throws IOException 86 */ getProgress()87 float getProgress() throws IOException; 88 } 89