最近，我正在学习mapreduce，并用它将数据写入mysql数据库。有两种方法，dboutputformat和sqoop。我尝试了第一个（请参阅此处），但遇到了一个问题，错误如下：

...
16/05/25 09:36:53 INFO mapred.LocalJobRunner: 3 / 3 copied.
16/05/25 09:36:53 INFO mapred.LocalJobRunner: reduce task executor complete.
16/05/25 09:36:53 WARN output.FileOutputCommitter: Output Path is null in cleanupJob()
16/05/25 09:36:53 WARN mapred.LocalJobRunner: job_local1404930626_0001
java.lang.Exception: java.io.IOException
    at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
    at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:529)
Caused by: java.io.IOException
    at org.apache.hadoop.mapreduce.lib.db.DBOutputFormat.getRecordWriter(DBOutputFormat.java:185)
    at org.apache.hadoop.mapred.ReduceTask$NewTrackingRecordWriter.<init>(ReduceTask.java:540)
    at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:614)
    at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:389)
    at org.apache.hadoop.mapred.LocalJobRunner$Job$ReduceTaskRunnable.run(LocalJobRunner.java:319)
    at java.util.concurrent.Executors$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)
16/05/25 09:36:54 INFO mapreduce.Job: Job job_local1404930626_0001 failed with state FAILED due to: NA
16/05/25 09:36:54 INFO mapreduce.Job: Counters: 38
File System Counters  
FILE: Number of bytes read=32583
    FILE: Number of bytes written=796446
    FILE: Number of read operations=0
    FILE: Number of large read operations=0
    FILE: Number of write operations=0
    HDFS: Number of bytes read=402
    HDFS: Number of bytes written=0
    HDFS: Number of read operations=18
    HDFS: Number of large read operations=0
    HDFS: Number of write operations=0
...

当我手动使用jdbc连接和插入数据时，结果证明是成功的。我注意到map/reduce任务执行器已经完成，但是它遇到了ioexception。所以我猜这个问题和数据库有关。
我的密码在这里。如果有人能帮我找出问题所在，我将不胜感激。
提前谢谢！