MapReduce 不产生输出

Question

我想对文本文件执行一个简单的 MapReduce，但它没有输出。这是我的代码：

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, "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(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

我在 jar 文件执行期间收到此错误：

17/05/07 23:10:53 WARN mapred.LocalJobRunner: job_local973452829_0001
java.lang.Exception:     org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in localfetcher#1
at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:529)
Caused by: org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in localfetcher#1
at org.apache.hadoop.mapreduce.task.reduce.Shuffle.run(Shuffle.java:134)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:376)
at org.apache.hadoop.mapred.LocalJobRunner$Job$ReduceTaskRunnable.run(LocalJobRunner.java:319)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.io.FileNotFoundException: /app/hadoop/tmp%20/mapred/local/localRunner/hduser/jobcache/job_local973452829_0001/attempt_local973452829_0001_m_000000_0/output/file.out.index
at org.apache.hadoop.fs.RawLocalFileSystem.open(RawLocalFileSystem.java:193)
at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:764)
at org.apache.hadoop.io.SecureIOUtils.openFSDataInputStream(SecureIOUtils.java:156)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:70)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:62)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:57)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.copyMapOutput(LocalFetcher.java:123)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.doCopy(LocalFetcher.java:101)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.run(LocalFetcher

我的代码有什么问题？我在 ubuntu 14.04 下，hadoop 2.4

Answer 1

尝试编写这样的 hdfs 命令

hadoop jar（jar文件名）（输入名）（输出名）

或者您是否在导出（jar 文件）之前检查过是否收到任何警告？

Answer 2

这是您的部分错误：

Caused by: java.io.FileNotFoundException: /app/hadoop/tmp%20/mapred/local/localRunner/hduser/jobcache/job_local973452829_0001/attempt_local973452829_0001_m_000000_0/output/file.out.index

我猜你的 core-site.xml 中的配置属性 hadoop.tmp.dir 有问题，因为 Hadoop 无法将临时输出文件（来自 Mapper）存储到你的磁盘。

您可以删除那个属性以便 hadoop 创建自己的临时目录来存储中间输出或将其设置为具有适当权限的某个目录。

MapReduce 不产生输出

MapReduce doesn't produce an output

java

hadoop

mapreduce

word-count