org.apache.hadoop.examples
Class WordCount.MapClass

java.lang.Object
  org.apache.hadoop.mapred.MapReduceBase
      org.apache.hadoop.examples.WordCount.MapClass

All Implemented Interfaces:

Closeable, JobConfigurable, Mapper<LongWritable,Text,Text,IntWritable>

Enclosing class:

WordCount

public static class WordCount.MapClass
extends MapReduceBase
implements Mapper<LongWritable,Text,Text,IntWritable>

Counts the words in each line. For each line of input, break the line into words and emit them as (word, 1).

Constructor Summary

WordCount.MapClass()

Method Summary

void	map(LongWritable key, Text value, OutputCollector<Text,IntWritable> output, Reporter reporter) Maps a single input key/value pair into an intermediate key/value pair.

Methods inherited from class org.apache.hadoop.mapred.MapReduceBase

close, configure

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.hadoop.mapred.JobConfigurable

configure

Methods inherited from interface java.io.Closeable

close

Constructor Detail

WordCount.MapClass

public WordCount.MapClass()

Method Detail

map

public void map(LongWritable key,
                Text value,
                OutputCollector<Text,IntWritable> output,
                Reporter reporter)
         throws IOException

Description copied from interface: Mapper

Maps a single input key/value pair into an intermediate key/value pair.

Output pairs need not be of the same types as input pairs. A given input pair may map to zero or many output pairs. Output pairs are collected with calls to OutputCollector.collect(Object,Object).

Applications can use the Reporter provided to report progress or just indicate that they are alive. In scenarios where the application takes an insignificant amount of time to process individual key/value pairs, this is crucial since the framework might assume that the task has timed-out and kill that task. The other way of avoiding this is to set mapred.task.timeout to a high-enough value (or even zero for no time-outs).

Specified by:

map in interface Mapper<LongWritable,Text,Text,IntWritable>

Parameters:

key - the input key.

value - the input value.

output - collects mapped keys and values.

reporter - facility to report progress.

Throws:

IOException