hadoop - 无法在mapreduce 2.x中运行wordcount示例

Question

我试图在Java中的mapreduce 2.x中执行mapreduce单词计数示例。...我创建了jar，但是在执行它时显示了错误，例如在包中未找到WordMapper类，但我在包中声明了该错误。 ....请帮助我解决问题...

这是我的WordCount驱动程序代码:

package com.mapreduce2.x;

public class WordCount {

public static void main(String args[]) throws IOException, ClassNotFoundException, InterruptedException
{
    Configuration conf=new Configuration();

    org.apache.hadoop.mapreduce.Job job= new org.apache.hadoop.mapreduce.Job(conf, "Word_Count");


    job.setMapperClass(WordMapper.class);
    job.setReducerClass(WordReducer.class);

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

    org.apache.hadoop.mapreduce.lib.input.FileInputFormat.setInputPaths(job, new Path(args[0]));
    org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.setOutputPath(job, new Path(args[1]));

    job.waitForCompletion(true);

}}

这是我的WordMapper类别:-

public class WordMapper extends Mapper<LongWritable, Text, Text,IntWritable>{

private final static IntWritable one=new IntWritable(1);
private Text word=new Text();

public void map(LongWritable key, Text value, org.apache.hadoop.mapreduce.Reducer.Context context) throws IOException, InterruptedException
{
    String line=value.toString();
    StringTokenizer tokenizer=new StringTokenizer(line);

    while(tokenizer.hasMoreTokens())
    {
        word.set(tokenizer.nextToken());
        context.write(word, one);

    }


}}

WordReducer代码-

public class WordReducer extends Reducer<Text, IntWritable, Text, IntWritable>{


public void reduce(Text key, Iterator<IntWritable> values,Context context) throws IOException, InterruptedException
{
    int sum =0;

    while(values.hasNext())
    {
        sum= sum+values.next().get();
    }

    context.write(key, new IntWritable(sum));
}}

它正在执行时显示以下错误-

15/05/29 10:12:26 INFO mapreduce.Job:  map 0% reduce 0%
15/05/29 10:12:33 INFO mapreduce.Job: Task Id : attempt_1432876892622_0005_m_000000_0, Status : FAILED
Error: java.lang.RuntimeException: java.lang.ClassNotFoundException: Class com.mapreduce2.x.WordMapper not found
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2076)
    at org.apache.hadoop.mapreduce.task.JobContextImpl.getMapperClass(JobContextImpl.java:186)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:742)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:163)
    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:1628)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)
Caused by: java.lang.ClassNotFoundException: Class com.mapreduce2.x.WordMapper not found
    at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:1982)
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2074)
    ... 8 more

Answer 1

在运行JAR文件时包括类名，或者可以在创建JAR文件时指定主类名。

如果运行时没有类名，则在运行JAR时指定类名。

使用命令
hadoop jar word.jar com.mapreduce2.x.WordMapper / input / output

这里的word.jar是JAR文件名。

要么

您还可以在创建jar文件时添加主类名称。
脚步:
文件->导出-> JAR->位置->然后单击下一步->要求选择主类->选择该类并单击确定

之后，您可以使用以下命令运行jar文件

hadoop jar word.jar /输入/输出

希望这能解决您的问题。