public class TokenCountMapper<K> extends MapReduceBase implements Mapper<K,Text,Text,LongWritable>
Mapper
that maps text values into StringTokenizer
to break text into tokens.构造器和说明 |
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TokenCountMapper() |
限定符和类型 | 方法和说明 |
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void |
map(K key,
Text value,
OutputCollector<Text,LongWritable> output,
Reporter reporter)
Maps a single input key/value pair into an intermediate key/value pair.
|
close, configure
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
configure
public void map(K key, Text value, OutputCollector<Text,LongWritable> output, Reporter reporter) throws IOException
Mapper
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).
map
在接口中 Mapper<K,Text,Text,LongWritable>
key
- the input key.value
- the input value.output
- collects mapped keys and values.reporter
- facility to report progress.IOException
Copyright © 2009 The Apache Software Foundation