Class Not Found Exception in Mapreduce wordcount job

Question

i am trying to run a wordcount job in hadoop.but always getting a class not found exception.I am posting the class that i wrote and the command i using to run the job

Answer 1

Though MapReduce program is parallel processing. Mapper, Combiner and Reducer class has sequence flow. Have to wait for completing each flow depends on other class so need job.waitForCompletion(true); But It must to set input and output path before starting Mapper, Combiner and Reducer class. Reference

Change your code like this:

 public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

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

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

    job.setJarByClass(WordCount.class);
    job.waitForCompletion(true);

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

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

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

I hope this will works.

Answer 2

try job.setJar("wordcount.jar");, where wordcount.jar is the jar file that you are going to package to. This method works for me, but NOT setJarByClass!

Answer 3

I suspect this :

14/01/27 13:16:02 WARN mapred.JobClient: No job jar file set. User classes may not be found. See JobConf(Class) or JobConf#setJar(String).

I got the same error when using CDH4.6 and it got solved after resolving the above warning.

Answer 4

Use The below code for resolving this Problem. job.setJarByClass(DriverClass.class);

Answer 5

Try adding this

Job job = new Job(conf, "wordcount");
job.setJarByClass(WordCount.class);

Answer 6

I also got the same issue and fixed it by removing same WordCount.class file in the same directory from where I am executing my jar. Looks like it is taking the class out side the jar. Try