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Java > Open Source Codes > net > nutch > mapReduce > Mapper


1 /* Copyright (c) 2005 The Nutch Organization. All rights reserved. */
2 /* Use subject to the conditions in http://www.nutch.org/LICENSE.txt. */
3
4 package net.nutch.mapReduce;
5
6 import java.io.IOException JavaDoc;
7
8 import net.nutch.io.Writable;
9 import net.nutch.io.WritableComparable;
10
11 /** Maps input key/value pairs to a set of intermediate key/value pairs. All
12  * intermediate values associated with a given output key are subsequently
13  * grouped by the map/reduce system, and passed to a {@link Reducer} to
14  * determine the final output.. */
15 public interface Mapper {
16   /** Maps a single input key/value pair into intermediate key/value pairs.
17    * Output pairs need not be of the same types as input pairs. A given input
18    * pair may map to zero or many output pairs. Output pairs are collected
19    * with calls to {@link
20    * OutputCollector#collect(WritableComparable,Writable)}.
21    *
22    * @param key the key
23    * @param value the values
24    * @param output collects mapped keys and values
25    */
26   void map(WritableComparable key, Writable value, OutputCollector output)
27     throws IOException JavaDoc;
28 }
29
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