Hadoop can not find the mapper class

Question

I am new to Hadoop and I want to run a MapReduce job. However, I've got the error that the hadoop can not find the mapper class. This is the error:

INFO mapred.JobClient: Task Id : attempt_201608292140_0023_m_000000_0, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: TransMapper1
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:857)
    at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:718)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:364)
    at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)

I checked the permission of my jar file and it is fine. Here it is the permission of the jar file:

-rwxrwxrwx.

Here it is the code for the code that launches the mapreduce job:

import java.io.File;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class mp{

public static void main(String[] args) throws Exception {

    Job job1 = new Job();
    job1.setJarByClass(mp.class);
    FileInputFormat.addInputPath(job1, new Path(args[0]));                  
    String oFolder = args[0] + "/output";
    FileOutputFormat.setOutputPath(job1, new Path(oFolder));
    job1.setMapperClass(TransMapper1.class);
    job1.setReducerClass(TransReducer1.class);
    job1.setMapOutputKeyClass(LongWritable.class);
    job1.setMapOutputValueClass(DnaWritable.class);
    job1.setOutputKeyClass(LongWritable.class);
    job1.setOutputValueClass(Text.class);
}
}

And here it is the mapper class (TransMapper1):

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class TransMapper1 extends  Mapper<LongWritable, Text, LongWritable, DnaWritable> {

    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {

        String line = value.toString();
        StringTokenizer tokenizer = new StringTokenizer(line);
        LongWritable bamWindow = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        LongWritable read = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        LongWritable refWindow = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        IntWritable chr = new IntWritable(Integer.parseInt(tokenizer.nextToken()));
        DoubleWritable dist = new DoubleWritable(Double.parseDouble(tokenizer.nextToken()));
        DnaWritable dnaW = new DnaWritable(bamWindow,read,refWindow,chr,dist);
        context.write(bamWindow,dnaW);
    }
}

I am compiling the package using following commands:

javac -classpath $MR_HADOOPJAR ${rootPath}mp/src/*.java
jar cvfm $mpJar $MR_MANIFEST ${rootPath}mp/src/*.class

This is the results of jar -tf mp/src/mp.jar command:

META-INF/
META-INF/MANIFEST.MF
mnt/miczfs/tide/mp/src/DnaWritable.class
mnt/miczfs/tide/mp/src/mp.class
mnt/miczfs/tide/mp/src/TransMapper1.class
mnt/miczfs/tide/mp/src/TransMapper2.class
mnt/miczfs/tide/mp/src/TransReducer1.class
mnt/miczfs/tide/mp/src/TransReducer2.class

And I am running the job with this:

mpJar=${rootPath}mp/src/mp.jar
mp_exec=mp
export HADOOP_CLASSPATH=$mpJar
hadoop $mp_exec <input path>

Also, I tried this command too:

hadoop jar $mp_exec <input path>

I changed the way I create the jar file into this command:

jar cf $mpJar $MR_MANIFEST ${rootPath}mp/src/*.class

And with this change, the the error has been changed to this:

Exception in thread "main" java.lang.ClassNotFoundException: mp
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:153)

So, before my problem was that the program can not find the mapper class, right now it can not find the main class!!! any thoughts??

Thank you guys

Answer 1

Running Mapreduce job from hadoop command requires jar file, mainclass and other args..

Usage: hadoop jar <jar> [mainClass] args...

So command for running your application jar should be:

hadoop jar $mpJar $mp_exec <inputpath>

Answer 2

HADOOP_CLASSPATH must specify the folder where the JAR file is located, due to which it is unable to find the class definition.