Cannot run jar file because of “Could not find or load main class”

问题

I have a test dir, which contains 3 folders:

--META-INF:
  one file MANIFEST.MF in the dir:
  MANIFEST.MF:
      anifest-Version: 1.0
      Created-By: 1.7.0_04-ea (Oracle Corporation)
      Class-Path: lib/*; .
      Main-Class: Setup.WordCount
-- lib:
   all the external jars I need for the project
-- Setup:
   3 files in the dir:
   WordCount$IntSumReducer.clas
   WordCount$TokenizerMapper.class
   WordCount.class

I create a jar file using the command

jar cmf test.jar test/META-INF/MANIFEST.MF test/Setup test/lib

but when I try to run the test.jar, an error reported:

Error: Could not find or load main class Setup.WordCount

I’ve tried to debug the prob for the whole day, still no idea!

WordCount.java:

package Setup;

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;
import org.apache.hadoop.util.GenericOptionsParser;

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();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err.println("Usage: wordcount <in> <out>");
      System.exit(2);
    }
    Job job = new Job(conf, "word count");
    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(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

The code is exactly the same as hadoop/example/WordCount, I’m trying to implementing hadoop example on my local dev environment.

回答1:

Your jar statement is slightly off. Try this:

jar -cfm test.jar test/META-INF/MANIFEST.MF -C test Setup -C test lib

Your command puts test/Setup/WordCount.class in the jar, which is why Java cannot find Setup/WordCount.class

You are also missing the package statement in the code you posted:

package Setup;

回答2:

specify package in code - and than use it in start command/ e.g.:

hadoop jar mywordcount.jar hadoop.mytest.WordCount input22/input /home/training/output

where hadoop.mytest.WordCount - is your package

来源：https://stackoverflow.com/questions/18971916/cannot-run-jar-file-because-of-could-not-find-or-load-main-class

标签

java

Hadoop

jar