我尝试运行本教程中关于hadoop管道的示例：
我在编译和其他方面都很成功。但是，在它运行之后，它会显示nullpointerexception错误。我试过很多方法，也读过很多类似的问题，但都找不到解决这个问题的方法。注意：我在一台虚拟分布式环境中的单机上运行。

hadoop pipes -D hadoop.pipes.java.recordreader=true -D hadoop.pipes.java.recordwriters=true -input /input -output /output -program /bin/wordcount
DEPRECATED: Use of this script to execute mapred command is deprecated.
Instead use the mapred command for it.

15/02/18 01:09:02 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
15/02/18 01:09:02 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
15/02/18 01:09:02 INFO jvm.JvmMetrics: Cannot initialize JVM Metrics with processName=JobTracker, sessionId= - already initialized
15/02/18 01:09:03 WARN mapreduce.JobSubmitter: No job jar file set.  User classes may not be found. See Job or Job#setJar(String).
15/02/18 01:09:04 INFO mapred.FileInputFormat: Total input paths to process : 1
15/02/18 01:09:04 INFO mapreduce.JobSubmitter: number of splits:1
15/02/18 01:09:04 INFO Configuration.deprecation: hadoop.pipes.java.recordreader is deprecated. Instead, use mapreduce.pipes.isjavarecordreader
15/02/18 01:09:04 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_local143452495_0001
15/02/18 01:09:06 INFO mapred.LocalDistributedCacheManager: Localized hdfs://localhost:9000/bin/wordcount as file:/tmp/hadoop-abdulrahman/mapred/local/1424214545411/wordcount
15/02/18 01:09:06 INFO mapreduce.Job: The url to track the job: http://localhost:8080/
15/02/18 01:09:06 INFO mapred.LocalJobRunner: OutputCommitter set in config null
15/02/18 01:09:06 INFO mapreduce.Job: Running job: job_local143452495_0001
15/02/18 01:09:06 INFO mapred.LocalJobRunner: OutputCommitter is org.apache.hadoop.mapred.FileOutputCommitter
15/02/18 01:09:06 INFO mapred.LocalJobRunner: Waiting for map tasks
15/02/18 01:09:06 INFO mapred.LocalJobRunner: Starting task: attempt_local143452495_0001_m_000000_0
15/02/18 01:09:06 INFO mapred.Task:  Using ResourceCalculatorProcessTree : [ ]
15/02/18 01:09:06 INFO mapred.MapTask: Processing split: hdfs://localhost:9000/input/data.txt:0+68
15/02/18 01:09:07 INFO mapred.MapTask: numReduceTasks: 1
15/02/18 01:09:07 INFO mapreduce.Job: Job job_local143452495_0001 running in uber mode : false
15/02/18 01:09:07 INFO mapreduce.Job:  map 0% reduce 0%
15/02/18 01:09:07 INFO mapred.MapTask: (EQUATOR) 0 kvi 26214396(104857584)
15/02/18 01:09:07 INFO mapred.MapTask: mapreduce.task.io.sort.mb: 100
15/02/18 01:09:07 INFO mapred.MapTask: soft limit at 83886080
15/02/18 01:09:07 INFO mapred.MapTask: bufstart = 0; bufvoid = 104857600
15/02/18 01:09:07 INFO mapred.MapTask: kvstart = 26214396; length = 6553600
15/02/18 01:09:07 INFO mapred.MapTask: Map output collector class = org.apache.hadoop.mapred.MapTask$MapOutputBuffer
15/02/18 01:09:08 INFO mapred.LocalJobRunner: map task executor complete.
15/02/18 01:09:08 WARN mapred.LocalJobRunner: job_local143452495_0001
java.lang.Exception: java.lang.NullPointerException
	at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
	at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:522)
Caused by: java.lang.NullPointerException
	at org.apache.hadoop.mapred.pipes.Application.<init>(Application.java:104)
	at org.apache.hadoop.mapred.pipes.PipesMapRunner.run(PipesMapRunner.java:69)
	at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:450)
	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:343)
	at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask.run(FutureTask.java:262)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
15/02/18 01:09:08 INFO mapreduce.Job: Job job_local143452495_0001 failed with state FAILED due to: NA
15/02/18 01:09:08 INFO mapreduce.Job: Counters: 0
Exception in thread "main" java.io.IOException: Job failed!
	at org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:836)
	at org.apache.hadoop.mapred.pipes.Submitter.runJob(Submitter.java:264)
	at org.apache.hadoop.mapred.pipes.Submitter.run(Submitter.java:503)
	at org.apache.hadoop.mapred.pipes.Submitter.main(Submitter.java:518)

编辑：我下载了hadoop的源代码并跟踪了异常发生的位置，似乎异常发生在初始化阶段，因此mapper/reducer中的代码并不是真正的问题。
hadoop中生成异常的函数如下：

/**Run a set of tasks and waits for them to complete. */
435     private void runTasks(List<RunnableWithThrowable> runnables,
436         ExecutorService service, String taskType) throws Exception {
437       // Start populating the executor with work units.
438       // They may begin running immediately (in other threads).
439       for (Runnable r : runnables) {
440         service.submit(r);
441       }
442 
443       try {
444         service.shutdown(); // Instructs queue to drain.
445 
446         // Wait for tasks to finish; do not use a time-based timeout.
447         // (See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6179024)
448         LOG.info("Waiting for " + taskType + " tasks");
449         service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
450       } catch (InterruptedException ie) {
451         // Cancel all threads.
452         service.shutdownNow();
453         throw ie;
454       }
455 
456       LOG.info(taskType + " task executor complete.");
457 
458       // After waiting for the tasks to complete, if any of these
459       // have thrown an exception, rethrow it now in the main thread context.
460       for (RunnableWithThrowable r : runnables) {
461         if (r.storedException != null) {
462           throw new Exception(r.storedException);
463         }
464       }
465     }

但问题是，它存储异常然后抛出它，这使我无法知道异常的实际来源。
有什么帮助吗？另外，如果你需要我张贴更多的细节，请让我知道。
谢谢您，