Hadoop Mapreduce word count Program

Question

I am new to Hadoop. Below is my code. I am getting the following error message when i run the Jar.

Input file (wordcount.txt) => this file is stored in "/home/cloudera/SK_JAR/jsonFile/wordcount.txt" path

Hello Hadoop, Goodbye Hadoop.

   package com.main;

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.LongWritable;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

public class WordCount {

    public static class Map extends Mapper {
        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();

        public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String line = value.toString();
            StringTokenizer tokenizer = new StringTokenizer(line);
            while (tokenizer.hasMoreTokens()) {
                word.set(tokenizer.nextToken());
                context.write(word, one);
            }
        }
     } 

     public static class Reduce extends Reducer {

        public void reduce(Text key, Iterable<IntWritable> values, Context context) 
          throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
     }


    public static void main(String[] args) throws IllegalArgumentException, IOException, ClassNotFoundException, InterruptedException {
        // TODO Auto-generated method stub

Configuration conf = new Configuration();


        Job job = new Job(conf, "wordcount");

    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);

    job.setMapperClass(Map.class);
    job.setReducerClass(Reduce.class);

    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputFormatClass(TextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));


//      job.waitForCompletion(true);
        System.exit(job.waitForCompletion(true) ?  0 : 1);


    }

}

Following is the error message. Can some one please help me on this?

let me know if you guys need more details..

hadoop jar Wordcount.jar WordCount '/home/cloudera/SK_JAR/jsonFile/wordcount.txt'  output

Error in laoding args file.java.io.FileNotFoundException: WordCount (No such file or directory)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:146)
    at java.io.FileInputStream.<init>(FileInputStream.java:101)
    at com.main.mainClass.main(mainClass.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.hadoop.util.RunJar.run(RunJar.java:221)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:136)

Answer 1

hadoop jar Wordcount.jar WordCount

Your main class is part of a package com.main therefore com.main.WordCount is needed to start your class.

You can open your JAR file as a ZIP file to verify if you can find com/main/WordCount$Map.class within it. If it is not there, then Eclipse is building your JAR wrong.

I might suggest you learn Maven, Gradle, or SBT to build a JAR rather than your IDE. In production, these are the tools commonly used to bundle Hadoop JAR files.

Answer 2

It seems main class file was not mentioned with your runnable jar file.

If you are using Eclipse to create jar file then follow below steps to create Wordcount.jar.

Right click on Project -> Export JAR file -> Click Next - > Uncheck all other resources. Then provide path for exporting .jar file -> Click Next -> Keep options selected -> Click Next and Finish. reference