MapReduce: WordCount Example | Phaisarn Sutheebanjard

Contents

1WordCount v1.0
1.1Source Code
1.2Usage
2Link

WordCount v1.0

This works with a local-standalone, pseudo-distributed or fully-distributed Hadoop installation.

Source Code

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&lt;Object, Text, Text, IntWritable&gt;{

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    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());
        context.write(word, one);
      }
    }
  }

  public static class IntSumReducer
       extends Reducer&lt;Text,IntWritable,Text,IntWritable&gt; {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable&lt;IntWritable&gt; values,
                       Context context
                       ) throws IOException, InterruptedException {
      int sum = 0;
      for (IntWritable val : values) {
        sum += val.get();
      }
      result.set(sum);
      context.write(key, result);
    }
  }

  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);
  }
}

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();

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());

context.write(word, one);

}

public static class IntSumReducer

extends Reducer<Text,IntWritable,Text,IntWritable> {

private IntWritable result = new IntWritable();

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);

}

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);

}

Usage

export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar

1	export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar

Compile WordCount.java:

$ hadoop com.sun.tools.javac.Main WordCount.java 
$ ls -l
-rw-r--r-- 1 hduser hadoop 1501 พ.ย. 23 15:55 WordCount.class
-rw-r--r-- 1 hduser hadoop 1739 พ.ย. 23 15:55 WordCount$IntSumReducer.class
-rw-r--r-- 1 hduser hadoop 2089 พ.ย. 23 15:54 WordCount.java
-rw-r--r-- 1 hduser hadoop 1736 พ.ย. 23 15:55 WordCount$TokenizerMapper.class

$ hadoop com.sun.tools.javac.Main WordCount.java

$ ls -l

-rw-r--r-- 1 hduser hadoop 1501 พ.ย. 23 15:55 WordCount.class

-rw-r--r-- 1 hduser hadoop 1739 พ.ย. 23 15:55 WordCount$IntSumReducer.class

-rw-r--r-- 1 hduser hadoop 2089 พ.ย. 23 15:54 WordCount.java

-rw-r--r-- 1 hduser hadoop 1736 พ.ย. 23 15:55 WordCount$TokenizerMapper.class

create a jar:

$ jar cf WordCount.jar WordCount*.class

1	$ jar cf WordCount.jar WordCount*.class

Sample text-files as input:

$ hadoop fs -ls input
-rw-r--r-- 1 hduser supergroup 22 2015-11-23 15:25 input/file01
-rw-r--r-- 1 hduser supergroup 28 2015-11-23 15:25 input/file02
$ hadoop fs -cat input/file01
Hello World Bye World
$ hadoop fs -cat input/file02
Hello Hadoop Goodbye Hadoop

$ hadoop fs -ls input

-rw-r--r-- 1 hduser supergroup 22 2015-11-23 15:25 input/file01

-rw-r--r-- 1 hduser supergroup 28 2015-11-23 15:25 input/file02

$ hadoop fs -cat input/file01

Hello World Bye World

$ hadoop fs -cat input/file02

Hello Hadoop Goodbye Hadoop

Run the application:

$ hadoop jar WordCount.jar WordCount input output
15/11/23 15:42:58 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
15/11/23 15:42:59 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
15/11/23 15:42:59 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
15/11/23 15:42:59 WARN mapreduce.JobResourceUploader: Hadoop command-line option parsing not performed. Implement the Tool interface and execute your application with ToolRunner to remedy this.
15/11/23 15:42:59 INFO input.FileInputFormat: Total input paths to process : 2
15/11/23 15:42:59 INFO mapreduce.JobSubmitter: number of splits:2
15/11/23 15:43:00 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_local1232649592_0001
15/11/23 15:43:00 INFO mapreduce.Job: The url to track the job: http://localhost:8080/
15/11/23 15:43:00 INFO mapreduce.Job: Running job: job_local1232649592_0001
15/11/23 15:43:00 INFO mapred.LocalJobRunner: OutputCommitter set in config null
   ...
   File Input Format Counters 
           Bytes Read=50
   File Output Format Counters 
           Bytes Written=41

$ hadoop jar WordCount.jar WordCount input output

15/11/23 15:42:58 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable

15/11/23 15:42:59 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id

15/11/23 15:42:59 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=

15/11/23 15:42:59 WARN mapreduce.JobResourceUploader: Hadoop command-line option parsing not performed. Implement the Tool interface and execute your application with ToolRunner to remedy this.

15/11/23 15:42:59 INFO input.FileInputFormat: Total input paths to process : 2

15/11/23 15:42:59 INFO mapreduce.JobSubmitter: number of splits:2

15/11/23 15:43:00 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_local1232649592_0001

15/11/23 15:43:00 INFO mapreduce.Job: The url to track the job: http://localhost:8080/

15/11/23 15:43:00 INFO mapreduce.Job: Running job: job_local1232649592_0001

15/11/23 15:43:00 INFO mapred.LocalJobRunner: OutputCommitter set in config null

...

File Input Format Counters

Bytes Read=50

File Output Format Counters

Bytes Written=41

Output:

$ hadoop fs -ls output
15/11/23 15:51:54 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Found 2 items
-rw-r--r-- 1 hduser supergroup 0 2015-11-23 15:26 output/_SUCCESS
-rw-r--r-- 1 hduser supergroup 41 2015-11-23 15:26 output/part-r-00000

$ hadoop fs -ls output

15/11/23 15:51:54 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable

Found 2 items

-rw-r--r-- 1 hduser supergroup 0 2015-11-23 15:26 output/_SUCCESS

-rw-r--r-- 1 hduser supergroup 41 2015-11-23 15:26 output/part-r-00000

$ hadoop fs -cat output/part-r-00000
15/11/23 15:52:19 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Bye 1
Goodbye 1
Hadoop 2
Hello 2
World 2

$ hadoop fs -cat output/part-r-00000

15/11/23 15:52:19 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable

Bye 1

Goodbye 1

Hadoop 2

Hello 2

World 2

Link

https://hadoop.apache.org/docs/current/hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduceTutorial.html#Example:_WordCount_v1.0