Question

线程中的异常＆＃34; main＆＃34;抛出java.lang.ClassNotFoundException：WordCount-＆GT;这么多的答案与这个问题有关，似乎我肯定错过了一个小点，这花了我几个小时来计算我将尝试尽可能清楚地了解路径，代码本身以及我尝试过的其他可能的解决方案我确信我正确配置了Hadoop，因为一切正常，直到最后一个阶段但仍然发布细节：

环境变量和路径

＆GT;

HADOOP VARIABLES START
export HADOOP_HOME=/usr/local/hadoop
export HADOOP_CONF_DIR=/usr/local/hadoop/etc/hadoop
export HADOOP_INSTALL=/usr/local/hadoop
export HADOOP_CLASSPATH=/usr/lib/jvm/java-8-oracle/lib/tools.jar
export PATH=$PATH:$HADOOP_INSTALL/bin
export PATH=$PATH:$HADOOP_INSTALL/sbin
export HADOOP_MAPRED_HOME=$HADOOP_HOME
export HADOOP_COMMON_HOME=$HADOOP_HOME
export HADOOP_HDFS_HOME=$HADOOP_HOME
export YARN_HOME=$HADOOP_HOME
#export HADOOP_COMMON_LIB_NATIVE_DIR=$HADOOP_INSTALL/lib/native
#export HADOOP_OPTS="-Djava.library.path=$HADOOP_INSTALL/lib"
export JAVA_HOME=/usr/lib/jvm/java-8-oracle
export PATH=$PATH:$HADOOP_HOME/bin
export PATH=$PATH:$JAVA_HOME/bin

#HADOOP VARIABLES END

班级本身：

package com.cloud.hw03;

/**
 * Hello world!
 *
 */
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;

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();
    Job job = Job.getInstance(conf, "wordcount");
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    job.setJarByClass(WordCount.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

我为编译和运行所做的工作：

使用我的WordCount maven项目（eclipse-workspace）在同一文件夹中创建jar文件

$ hadoop com.sun.tools.javac.Main WordCount.java

$ jar cf WordCount.jar WordCount * .class
运行程序:(我已经在hdfs中创建了一个目录并复制了输入输出文件）

hadoop jar WordCount.jar WordCount / input / inputfile01 / input / outputfile01

结果是：线程中的异常＆＃34; main＆＃34; java.lang.ClassNotFoundException：WordCount

由于我与WordCount.class位于同一目录，并且我在同一目录中创建了我的jar文件，我没有指定WordCount的完整路径，所以我在这个目录中运行上面的第二个命令：

我已经添加了job.setJarByClass（WordCount.class）;到代码所以没有帮助。我很感激你花时间回答！我确信我再做一些意想不到的事情，并且无法弄清楚4小时

Answer 1

Hadoop网站上的Wordcount示例代码不使用包

既然你有一个，你就可以运行完全限定的类。与常规Java应用程序完全相同

hadoop jar WordCount.jar com.cloud.hw03.WordCount

另外，如果你实际上有一个Maven项目，那么hadoop com.sun.tools.javac.Main是不正确的。您实际上将使用Maven来编译和创建包含所有类的JAR，而不仅仅是WordCount*个文件

例如，从包含pom.xml的文件夹

mvn package

否则，您需要位于父目录

中

hadoop com.sun.tools.javac.Main ./com/cloud/hw03/WordCount.java

并从该目录运行jar cf命令

无法找到Hadoop Java类

1 个答案: