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.         


        

Answer 1

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 

Answer 2

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

Answer 3

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?

Answer 4

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

Answer 5

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.

Answer 6

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