word.set() 方法在 map reduce hadoop 中抛出空指针异常

Question

我是 map reduce 编程的新手，我从简单的字数示例开始我的课程。但是，我正在尝试一种不同的方法。我的 hdfs 输入文件夹中有两个输入文件。我正在尝试生成像

这样的输出

anyword1 --> filename1     2
anyword2 --> filename2     3

我编写了一个映射器类来在 Key 处将单词和文件名连接在一起，但是当我在 Text 中设置键值时，它会引发空指针异常。有人可以帮助并建议我在哪里做错了。

我的映射器类

public static class TokenizerMapper 
       extends Mapper<Object, Text, Text,IntWritable>{

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

    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      StringTokenizer itr = new StringTokenizer(value.toString());
      String fileName = ((FileSplit) context.getInputSplit()).getPath().getName();
      String modifiedWord ="";
      fileName = "-->"+fileName;
      System.out.println("filename before word-->"+fileName);
      while (itr.hasMoreTokens()) {
        modifiedWord = itr.nextToken().toString();//+fileName;
        modifiedWord = modifiedWord + fileName;
        System.out.println("modified word-->"+modifiedWord);
        word.set(modifiedWord);
        context.write(word, one);
        System.out.println("Mapper context-->"+word);
      }
    }
  }

--------例外----

[root@LinuxCentos7 hadoop]# hadoop jar /usr/local/mapreduceexample/WordCountEx3.jar /user/Siddharth/Input /user/Siddharth/output
17/06/09 23:32:29 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032
17/06/09 23:32:32 INFO input.FileInputFormat: Total input paths to process : 2
17/06/09 23:32:32 INFO mapreduce.JobSubmitter: number of splits:2
17/06/09 23:32:32 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1497025644387_0011
17/06/09 23:32:33 INFO impl.YarnClientImpl: Submitted application application_1497025644387_0011
17/06/09 23:32:33 INFO mapreduce.Job: The url to track the job: http://LinuxCentos7:8088/proxy/application_1497025644387_0011/
17/06/09 23:32:33 INFO mapreduce.Job: Running job: job_1497025644387_0011
17/06/09 23:32:52 INFO mapreduce.Job: Job job_1497025644387_0011 running in uber mode : false
17/06/09 23:32:52 INFO mapreduce.Job:  map 0% reduce 0%
17/06/09 23:33:16 INFO mapreduce.Job:  map 100% reduce 0%
17/06/09 23:33:16 INFO mapreduce.Job: Task Id : attempt_1497025644387_0011_m_000000_0, Status : FAILED
Error: java.lang.NullPointerException
    at com.hadoop.WordCountEx3$TokenizerMapper.map(WordCountEx3.java:56)
    at com.hadoop.WordCountEx3$TokenizerMapper.map(WordCountEx3.java:1)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:146)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:787)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:164)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)

Answer 1

使用Text 实例初始化word 变量：

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

public void map(Object key, Text value, Context context)
        throws IOException, InterruptedException {
    ...
}