Nullpointer exception in HBase MapReduce

问题

I have a mapreduce app that takes an HBase source data and mapreduces it to another HBase table, all written in Java.When I run it using

hadoop jar myhbase.jar 

It terminated with a NullpointerException as below:

14/01/31 11:07:02 INFO zookeeper.ClientCnxn: Socket connection established to 127.0.0.1/127.0.0.1:2181, initiating session
14/01/31 11:07:02 INFO zookeeper.ClientCnxn: Session establishment complete on server 127.0.0.1/127.0.0.1:2181, sessionid = 0x143e677d6e30007, negotiated timeout = 180000
14/01/31 11:07:03 INFO mapreduce.TableOutputFormat: Created table instance for hourinfo
14/01/31 11:07:03 INFO mapred.JobClient: Cleaning up the staging area hdfs://192.168.1.149:9000/hadoop_tmp/mapred/staging/root/.staging/job_201401310933_0002
Exception in thread "main" java.lang.NullPointerException
        at org.apache.hadoop.net.DNS.reverseDns(DNS.java:72)
        at org.apache.hadoop.hbase.mapreduce.TableInputFormatBase.reverseDNS(TableInputFormatBase.java:219)
        at org.apache.hadoop.hbase.mapreduce.TableInputFormatBase.getSplits(TableInputFormatBase.java:184)
        at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:962)
        at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:979)
        at org.apache.hadoop.mapred.JobClient.access$600(JobClient.java:174)
        at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:897)
        at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:850)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
        at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:850)
        at org.apache.hadoop.mapreduce.Job.submit(Job.java:500)
        at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:530)
        at mapreduce.hi.api.hbase.HBaseJobRunner.main(HBaseJobRunner.java:37)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.util.RunJar.main(RunJar.java:156)

I am using hbase-0.94.5 and hadoop-1.0.4. I am really stuck on this error.Please help..

回答1:

Check out the top of your stack trace:

 at org.apache.hadoop.net.DNS.reverseDns(DNS.java:72)

Be sure that your forward and reverse DNS lookups exactly match on your HBase/ZK nodes.

回答2:

Okay I fixed the issue. From the exception I got it originated from TableInputFormatBase.getSplits() .When I analyze source code of TableInputFormatBase, it is looking for a job configuration parameter hbase.nameserver.address . When I set this value from my code, it worked.

来源：https://stackoverflow.com/questions/21480858/nullpointer-exception-in-hbase-mapreduce