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courses:mapreduce-tutorial:step-24 [2012/01/27 21:32]
straka
courses:mapreduce-tutorial:step-24 [2012/01/27 21:41]
straka
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 ====== MapReduce Tutorial : Mappers, running Java Hadoop jobs ====== ====== MapReduce Tutorial : Mappers, running Java Hadoop jobs ======
  
-We start by exploring a simple Hadoop job with Mapper only. The Mapper outputs only keys starting with ''A''.+We start by going through a simple Hadoop job with Mapper only. 
 + 
 +A mapper which processes (key, value) pairs of types (Kin, Vin) and produces (key, value) pairs of types (Kout, Vout) must be a subclass of [[http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Mapper.html|Mapper<Kin, Vin, Kout, Vout>]]. In our case, ''TheMapper'' is subclass of ''Mapper<Text, Text, Text, Text>''
 + 
 + 
 +http://hadoop.apache.org/common/docs/r1.0.0/api/org/apache/hadoop/mapreduce/Mapper.html 
 + 
 + The Mapper outputs only keys starting with ''A''. 
 <file java MapperOnlyHadoopJob.java> <file java MapperOnlyHadoopJob.java>
 import java.io.IOException; import java.io.IOException;
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 } }
 </file> </file>
- 
-A mapper which processes (key, value) pairs of types (Kin, Vin) and produces (key, value) pairs of types (Kout, Vout) must be a subclass of ''Mapper<Kin, Vin, Kout, Vout>''. In our case, ''TheMapper'' is subclass of ''Mapper<Text, Text, Text, Text>''. 
  
 ===== Running the job ===== ===== Running the job =====

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