Hadoop: Contoh Program Sederhana

Sumber:

• http://www.drdobbs.com/database/hadoop-writing-and-running-your-first-pr/240153197
• https://hadoop.apache.org/docs/r1.2.1/mapred_tutorial.html

Source Code

Contoh source code WordCount.java untuk menghitung jumlah masing-masing kata dari sebuah input set.

cd ~
vi WordCount.java

package org.myorg;

import java.io.IOException;
import java.util.*;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;
	
public class WordCount {
	
   public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
     private final static IntWritable one = new IntWritable(1);
     private Text word = new Text();

     public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
       String line = value.toString();
       StringTokenizer tokenizer = new StringTokenizer(line);
       while (tokenizer.hasMoreTokens()) {
         word.set(tokenizer.nextToken());
         output.collect(word, one);
       }
     }
   }

   public static class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
     public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {
       int sum = 0;
       while (values.hasNext()) {
         sum += values.next().get();
       }
       output.collect(key, new IntWritable(sum));
     }
   }

   public static void main(String[] args) throws Exception {
     JobConf conf = new JobConf(WordCount.class);
     conf.setJobName("wordcount"); 
	
     conf.setOutputKeyClass(Text.class);
     conf.setOutputValueClass(IntWritable.class);

     conf.setMapperClass(Map.class);
     conf.setCombinerClass(Reduce.class);
     conf.setReducerClass(Reduce.class);

     conf.setInputFormat(TextInputFormat.class);
     conf.setOutputFormat(TextOutputFormat.class);

     FileInputFormat.setInputPaths(conf, new Path(args[0]));
     FileOutputFormat.setOutputPath(conf, new Path(args[1]));

     JobClient.runJob(conf);
   }
}

Compile

Asumsinya HADOOP_HOME adalah root instalasi dan HADOOP_VERSION adalah versi Hadoop yang di install, compile WordCount.java dan buat jar:

export HADOOP_HOME=/usr/local/hadoop/share/hadoop/common
export HADOOP_VERSION=2.7.1

mkdir wordcount_classes
javac -classpath ${HADOOP_HOME}/hadoop-common-${HADOOP_VERSION}.jar -d wordcount_classes WordCount.java
jar -cvf /usr/joe/wordcount.jar -C wordcount_classes/ .

Penggunaan

Asumsi

/usr/joe/wordcount/input - input directory di HDFS
/usr/joe/wordcount/output - output directory di HDFS

Sample text-files as input:

bin/hadoop dfs -ls /usr/joe/wordcount/input/
/usr/joe/wordcount/input/file01
/usr/joe/wordcount/input/file02

bin/hadoop dfs -cat /usr/joe/wordcount/input/file01
Hello World Bye World

bin/hadoop dfs -cat /usr/joe/wordcount/input/file02
Hello Hadoop Goodbye Hadoop 

Jalankan aplikasi

bin/hadoop jar /usr/joe/wordcount.jar org.myorg.WordCount /usr/joe/wordcount/input /usr/joe/wordcount/output

Output:

bin/hadoop dfs -cat /usr/joe/wordcount/output/part-00000
Bye 1
Goodbye 1
Hadoop 2
Hello 2
World 2 

Referensi

• http://www.drdobbs.com/database/hadoop-writing-and-running-your-first-pr/240153197
• http://www.drdobbs.com/database/hadoop-writing-and-running-your-first-pr/240153197?pgno=2
• https://hadoop.apache.org/docs/r1.2.1/mapred_tutorial.html