Why hadoop does not recognize my Map class?

问题

I am trying to run my PDFWordCount map-reduce program on hadoop 2.2.0 but I get this error:

13/12/25 23:37:26 INFO mapreduce.Job: Task Id : attempt_1388041362368_0003_m_000009_2, Status : FAILED
Error: java.lang.RuntimeException: java.lang.ClassNotFoundException: Class PDFWordCount$MyMap not found
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:1720)
    at org.apache.hadoop.mapreduce.task.JobContextImpl.getMapperClass(JobContextImpl.java:186)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:721)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:162)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:415)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1491)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:157)
Caused by: java.lang.ClassNotFoundException: Class PDFWordCount$MyMap not found
    at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:1626)
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:1718)
    ... 8 more

It says that my map class is not known. I have a cluster with a namenod and 2 datanodes on 3 VMs.

My main function is this:

public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    @SuppressWarnings("deprecation")
    Job job = new Job(conf, "wordcount");

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

    job.setMapperClass(MyMap.class);
    job.setReducerClass(MyReduce.class);

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

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

    job.setJarByClass(PDFWordCount.class);
    job.waitForCompletion(true);
  }

If I run my jar using this command:

yarn jar myjar.jar PDFWordCount /in /out

it takes /in as output path and gives me error while I have job.setJarByClass(PDFWordCount.class); in my main function as you see above.

I have run simple WordCount project with main function exactly like this main function and to run it, I used yarn jar wc.jar MyWordCount /in2 /out2 and it run flawlessly.

I can't understand what is the problem!

UPDATE: I tried to move my work from this project to wordcount project I have used successfully. I built a package, copied related files from pdfwordcount project to this package and exported the project (my main was not changed to used PDFInputFormat, so I did nothing except moving java files to new package.) It didn't work. I deleted files from other project but it didn't work. I moved java file back to default package but it didn't work!

What's wrong?!

回答1:

I found a way to overcome this problem, even though I couldn't understand what was the problem actually.

When I want to export my java project as a jar file in eclipse, I have two options:

Extract required libraries into generated JAR
Package required libraries into generated JAR

I don't know exactly what is the difference or is it a big deal or not. I used to choose second option, but if I choose first option, I can run my job using this command:

yarn jar pdf.jar /in /out

来源：https://stackoverflow.com/questions/20781120/why-hadoop-does-not-recognize-my-map-class

标签

java

Hadoop

MapReduce

runtimeexception