Hadoop Java Error : Exception in thread "main" java.lang.NoClassDefFoundError: WordCount (wrong name: org/myorg/WordCount)

Question

I am new to hadoop. I followed the maichel-noll tutorial to set up hadoop in single node.I tried running WordCount program. This is the code I used:

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, "WordCount");
    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);
  }
}

This is what I get when I try running it.

hduser@aswin-HP-Pavilion-15-Notebook-PC:/usr/local/hadoop$ bin/hadoop jar wc.jar WordCount /home/hduser/gutenberg /home/hduser/gutenberg-output/sample.txt
Exception in thread "main" java.lang.NoClassDefFoundError: WordCount (wrong name: org/myorg/WordCount)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:788)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:447)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:270)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:205)

Can anyone please help me. My class path :

hduser@aswin-HP-Pavilion-15-Notebook-PC:/usr/local/hadoop$ hadoop classpath
/usr/local/hadoop/etc/hadoop:/usr/local/hadoop/share/hadoop/common/lib/*:/usr/local/hadoop/share/hadoop/common/*:/usr/local/hadoop/share/hadoop/hdfs:/usr/local/hadoop/share/hadoop/hdfs/lib/*:/usr/local/hadoop/share/hadoop/hdfs/*:/usr/local/hadoop/share/hadoop/yarn/lib/*:/usr/local/hadoop/share/hadoop/yarn/*:/usr/local/hadoop/share/hadoop/mapreduce/lib/*:/usr/local/hadoop/share/hadoop/mapreduce/*:/usr/lib/jvm/java-7-openjdk-i386/lib/tools.jar:/usr/local/hadoop/contrib/capacity-scheduler/*.jar

You are missing Driver class (although you combined it with reducer which is bad practice). Btw do you have this jar in your classpath? — SMA
– SMA, Commented Nov 2, 2014 at 15:26
Have added the class path in the question. Should I place the jar file in one of the above folder. — Aswin Alagappan
– Aswin Alagappan, Commented Nov 2, 2014 at 15:35
No place it in same directory from where you are running your mapred or place it in lib directory where hadoop libs sits. — SMA
– SMA, Commented Nov 2, 2014 at 15:44
I tried placing it in lib and also share/lib/mapreduce. Still the same error. — Aswin Alagappan
– Aswin Alagappan, Commented Nov 2, 2014 at 15:54
just saw this "org/myorg" you are using package so use org.myorg.WordCount so your command would be: bin/hadoop jar wc.jar org.myorg.WordCount /home/hduser/gutenberg /home/hduser/gutenberg-output/sample.txt — SMA
– SMA, Commented Nov 2, 2014 at 15:56

Kishore · Accepted Answer · 2014-11-02 18:10:00Z

10

try this,

import java.io.IOException;
import java.util.Iterator;
import java.util.StringTokenizer;

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.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileOutputFormat;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.TextInputFormat;
import org.apache.hadoop.mapred.TextOutputFormat;

public class WordCount {

    public static class Map extends MapReduceBase implements
            Mapper<LongWritable, Text, Text, IntWritable> {

        @Override
        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()) {
                value.set(tokenizer.nextToken());
                output.collect(value, new IntWritable(1));
            }

        }
    }

    public static class Reduce extends MapReduceBase implements
            Reducer<Text, IntWritable, Text, IntWritable> {

        @Override
        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.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);

    }
}

then run command

bin/hadoop jar WordCount.jar WordCount /hdfs_Input_filename /output_filename

if your code is in particular package then you have to mention package name with class name

bin/hadoop jar WordCount.jar PakageName.WordCount /hdfs_Input_filename /output_filename

answered Nov 2, 2014 at 18:10

Kishore

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5 Comments

Aswin Alagappan Over a year ago

I get the same No class def found error. Btw, this is how I compile and create jar. Is this rite : $ bin/hadoop com.sun.tools.javac.Main WordCount.java $ jar cf wc.jar WordCount*.class

Kishore Over a year ago

What's problem with your code, your program is in particular package or in default package in eclipse???

Aswin Alagappan Over a year ago

Just look at my solution. I know its crazy :D . Thanks a lot. I actually used your code. :)

Zahra Over a year ago

your answer is missing the explanation as to why the above didn't work OR why your solution works!

SRIDHARAN Over a year ago

@KishoreKumarSuthar can you suggest some good tutorials for mapreduce?

Aswin Alagappan · Accepted Answer · 2014-11-02 18:56:48Z

1

This may sound crazy. I added package org.myorg; to my code and compiled it again. I placed the class files in org/myorg folder and created the jar file using them. Then I ran using the jar wc.jar org.myorg.WordCount command and it got executed successfully. It would be nice if someone could explain me how it actually ran :D . Any way, thanks a lot for helping me guys.

answered Nov 2, 2014 at 18:56

Aswin Alagappan

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Comments

Zahra · Accepted Answer · 2016-01-08 00:45:20Z

1

try explicitly including the nested classes(i.e. TokenizerMapper and IntSumReducer) in you jar file. Here is how I did it:

jar cvf WordCount.jar WordCount.class WordCount\$TokenizerMapper.class WordCount\$IntSumReducer.class

answered Jan 8, 2016 at 0:45

Zahra

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1 Comment

Alex Over a year ago

This did it for me. The error I was getting was "NoClassDefFoundError: TokenizerMapper"

Holiday Tom · Accepted Answer · 2021-06-06 03:00:17Z

1

there is something wrong with packaging. you should try this:

jar cf wc.jar WordCount*.class

notice there is a symbol '*'

edited Jun 6, 2021 at 3:00

answered May 1, 2021 at 4:34

Holiday Tom

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Comments

SMA · Accepted Answer · 2014-11-02 15:59:18Z

0

You are using package in your class. So your command should be

bin/hadoop jar wc.jar org.myorg.WordCount /home/hduser/gutenberg /home/hduser/gutenberg-output/sample.txt

answered Nov 2, 2014 at 15:59

SMA

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1 Comment

Aswin Alagappan Over a year ago

I get a class not found exception. Exception in thread "main" java.lang.ClassNotFoundException: org.myorg.WordCount

Norman Bai · Accepted Answer · 2015-12-20 04:41:07Z

0

I think you made a mistake here :

/usr/local/hadoop$ bin/hadoop jar wc.jar WordCount /home/hduser/gutenberg /home/hduser/gutenberg-output/sample.txt

please change it to :

/usr/local/hadoop$ bin/hadoop jar wc.jar org.myorg.WordCount /home/hduser/gutenberg /home/hduser/gutenberg-output/sample.txt

that should work.

@Aswin Alagappan : Reason is a jar file cotains your path in it. JVM cannot find your class in the jar file becase it is in the "jar\org\myorg" path. Understand?

answered Dec 20, 2015 at 4:41

Norman Bai

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Comments

Colonna Maurizio · Accepted Answer · 2019-09-07 08:18:06Z

The answer of Kishore, allowed me to go in the right direction, if it’s possible i want to confirm this, reporting what I did about an experiiment with java code on moltiplication of sparse matrix :

1) Source code (downloaded from https://github.com/marufaytekin/MatrixMultiply/tree/master/src/main/java/com/lendap/hadoop), and saved in /home/hduser/playground/src/matrixMult

2) Downloaded datasets (matrix M and N from https://github.com/marufaytekin/MatrixMultiply/tree/master/input), and then saved in HDFS, with the following path : /user/hduser/inMatrix

3) Compilation with hadoop classes, with creation of java Classes in playground/classes5 : javac -classpath $HADOOP_HOME/share/hadoop/common/lib/activation-1.1.jar:$HADOOP_HOME/share/hadoop/common/hadoop-common-2.7.1.jar:/usr/hadoop/hadoop-2.7.1/share/hadoop/mapreduce/* -d playground/classes5 playground/src/matrixMult/*

4) Creation of jar file MatrixMultiply.jar with the following command : jar -cvf playground/MatrixMultiply.jar -C playground/classes5/ .

5) hadoop mapReduce command (from the $HADOOP_HOME path, that in my case is /usr/hadoop/hadoop-2.7.1$ hadoop jar /home/hduser/playground/MatrixMultiply.jar com.lendap.hadoop.MatrixMultiply /user/hduser/inMatrix/ outputMatrix

6) Correct execution of mapreduce job on my 4 nodes cluster. Here, part of the final output :

0,375,890.0 0,376,1005.0 0,377,1377.0 0,378,604.0 0,379,924.0 0,38,476.0 0,380,621.0 0,381,730.0

990,225,542.0 990,226,639.0 990,227,466.0 990,228,406.0 990,229,343.0 990,23,397.0 990,230,794.0

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