1.原因：沒有控制語句導致的迭代器的越界，使得map中的數據無法傳入reduce，從而無法把結果傳入目標文件中。
在進行Mapreduce實例——WordCount實驗時遇到的錯誤，開始以為是lib包導入和讀取源文件格式的問題，后來無論怎么修改都會報這個錯誤，報錯如下：
java.lang.Exception: java.util.NoSuchElementException
at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:491)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:551)
Caused by: java.util.NoSuchElementException
at java.util.StringTokenizer.nextToken(StringTokenizer.java:349)
at mapreduce.WordCount$doMapper.map(WordCount.java:43)
at mapreduce.WordCount$doMapper.map(WordCount.java:1)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:146)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:793)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:270)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:473)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
at java.lang.Thread.run(Thread.java:748)
18/11/16 00:25:39 INFO mapreduce.Job: Job job_local1205845239_0001 failed with state FAILED due to: NA
18/11/16 00:25:39 INFO mapreduce.Job: Counters: 0
錯誤根源：
2.解決方案：
解決方案1
if(tokenizer.hasMoreTokens()) { this.word.set(tokenizer.nextToken()); context.write(this.word, one); }
解決方案2
if(!value.toString().equals("")) { word.set(tokenizer.nextToken()); context.write(word, one); }