Created
December 12, 2014 02:13
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import java.io.IOException; | |
import java.util.StringTokenizer; | |
import org.apache.hadoop.conf.Configuration; | |
import org.apache.hadoop.fs.Path; | |
import org.apache.hadoop.io.IntWritable; | |
import org.apache.hadoop.io.Text; | |
import org.apache.hadoop.mapreduce.Job; | |
import org.apache.hadoop.mapreduce.Mapper; | |
import org.apache.hadoop.mapreduce.Reducer; | |
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; | |
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; | |
public class WordCount { | |
public static class TokenizerMapper | |
extends Mapper<Object, Text, Text, IntWritable>{ | |
private final static IntWritable one = new IntWritable(1); | |
private Text word = new Text(); | |
/* | |
* Mapper: takes lines of text, breaks them down into lowercase words and | |
* emits a (key,value) pair for each word, key being the word and | |
* value being `1`. For example, `one two two three three three` will emit: | |
* (one, 1) | |
* (two, 1) | |
* (two, 1) | |
*/ | |
public void map(Object key, Text value, Context context) throws IOException, InterruptedException { | |
StringTokenizer itr = new StringTokenizer(value.toString()); | |
while (itr.hasMoreTokens()) { | |
word.set(itr.nextToken().toLowerCase()); | |
context.write(word, one); | |
} | |
} | |
} | |
public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable> { | |
private IntWritable result = new IntWritable(); | |
/* | |
* Reducer: takes a word (key) and a list of int's (`1`'s) and returns | |
* a pair of (word, sum), with sum being the sum of all the list's values | |
* -- hence, the frequency. For example, (`two`, [1,1]) from above will emit | |
* (`two`, 2) | |
*/ | |
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { | |
int sum = 0; | |
for (IntWritable val : values) { | |
sum += val.get(); | |
} | |
result.set(sum); | |
context.write(key, result); | |
} | |
} | |
/* | |
* Main driver: Creates a hadoop job, configures mapper, reducer, | |
* output types, files for input and output and | |
* runs the task. | |
*/ | |
public static void main(String[] args) throws Exception { | |
Configuration conf = new Configuration(); | |
Job job = Job.getInstance(conf, "word count"); | |
job.setJarByClass(WordCount.class); | |
job.setMapperClass(TokenizerMapper.class); | |
// job.setCombinerClass(IntSumReducer.class); | |
job.setReducerClass(IntSumReducer.class); | |
job.setOutputKeyClass(Text.class); | |
job.setOutputValueClass(IntWritable.class); | |
FileInputFormat.addInputPath(job, new Path(args[0])); | |
FileOutputFormat.setOutputPath(job, new Path(args[1])); | |
System.exit(job.waitForCompletion(true) ? 0 : 1); | |
} | |
} |
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