空指针异常

Question

我有一个MapReduce的应用程序，需要一个HBase的源数据，并将其mapreduces另一个HBase的表，全部写在Java.When我使用

hadoop jar myhbase.jar 

它终止了与一个NullpointerException 运行如下图所示：

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) 

我使用hbase-0.94.5和hadoop-1.0.4。我真的被困在此error.Please帮助..

Answer 1

好的，我解决了这个问题。从异常我得到它起源于TableInputFormatBase.getSplits()。当我分析TableInputFormatBase的源代码时，它正在寻找作业配置参数hbase.nameserver.address。当我从我的代码中设置这个值时，它工作。

Answer 2

退房您的堆栈跟踪的顶部：

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

确保您的正向和反向DNS查找完全匹配您的HBase/ZK节点。