java - 由于 “Could not find or load main class”而无法运行jar文件

Question

我有一个测试目录，其中包含3个文件夹:

--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

我使用以下命令创建一个jar文件

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

但是当我尝试运行test.jar时，报告了一个错误:

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

我已经整天尝试调试问题了，还是不知道!
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);
  }
}

该代码与hadoop/example/WordCount完全相同，我正在尝试在本地开发环境中实现hadoop示例。

Answer 1

您的jar语句略有偏离。试试这个:

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

您的命令将test / Setup / WordCount.class放入jar中，这就是Java无法找到Setup / WordCount.class的原因

您还缺少发布的代码中的package语句:

package Setup;