| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.hadoop.mapred; |
| |
| import java.io.IOException; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** |
| * <code>RecordReader</code> reads <key, value> pairs from an |
| * {@link InputSplit}. |
| * |
| * <p><code>RecordReader</code>, typically, converts the byte-oriented view of |
| * the input, provided by the <code>InputSplit</code>, and presents a |
| * record-oriented view for the {@link Mapper} & {@link Reducer} tasks for |
| * processing. It thus assumes the responsibility of processing record |
| * boundaries and presenting the tasks with keys and values.</p> |
| * |
| * @see InputSplit |
| * @see InputFormat |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public interface RecordReader<K, V> { |
| /** |
| * Reads the next key/value pair from the input for processing. |
| * |
| * @param key the key to read data into |
| * @param value the value to read data into |
| * @return true iff a key/value was read, false if at EOF |
| */ |
| boolean next(K key, V value) throws IOException; |
| |
| /** |
| * Create an object of the appropriate type to be used as a key. |
| * |
| * @return a new key object. |
| */ |
| K createKey(); |
| |
| /** |
| * Create an object of the appropriate type to be used as a value. |
| * |
| * @return a new value object. |
| */ |
| V createValue(); |
| |
| /** |
| * Returns the current position in the input. |
| * |
| * @return the current position in the input. |
| * @throws IOException |
| */ |
| long getPos() throws IOException; |
| |
| /** |
| * Close this {@link InputSplit} to future operations. |
| * |
| * @throws IOException |
| */ |
| public void close() throws IOException; |
| |
| /** |
| * How much of the input has the {@link RecordReader} consumed i.e. |
| * has been processed by? |
| * |
| * @return progress from <code>0.0</code> to <code>1.0</code>. |
| * @throws IOException |
| */ |
| float getProgress() throws IOException; |
| } |