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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3271) Using webhdfs in a flink topology throws classnotfound exception
Date Mon, 01 Feb 2016 15:52:39 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15126432#comment-15126432

ASF GitHub Bot commented on FLINK-3271:

Github user abhishekagarwal87 commented on the pull request:

    Hi @StephanEwen 
    how does separating out hadoop classes solve the classloader problem? Since even if the
jars are different, they will be loaded in parent classloader and application jar is in child

> Using webhdfs in a flink topology throws classnotfound exception
> ----------------------------------------------------------------
>                 Key: FLINK-3271
>                 URL: https://issues.apache.org/jira/browse/FLINK-3271
>             Project: Flink
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.10.1
>            Reporter: Abhishek Agarwal
>            Assignee: Abhishek Agarwal
> I was just trying to run a storm topology on flink using flink-storm. I got this exception
> {noformat}
> Caused by: java.lang.NoClassDefFoundError: org/mortbay/util/ajax/JSON
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem.jsonParse(WebHdfsFileSystem.java:325)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem$FsPathResponseRunner.getResponse(WebHdfsFileSystem.java:727)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem$AbstractRunner.runWithRetry(WebHdfsFileSystem.java:610)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem$AbstractRunner.access$100(WebHdfsFileSystem.java:458)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem$AbstractRunner$1.run(WebHdfsFileSystem.java:487)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at javax.security.auth.Subject.doAs(Subject.java:422)
> 	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1628)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem$AbstractRunner.run(WebHdfsFileSystem.java:483)
> 	at org.apache.hadoop.hdfs.web.WebHdfsFileSystem.listStatus(WebHdfsFileSystem.java:1277)
> {noformat}
> My topology list some files on hdfs using webhdfs API. org.mortbay.util.ajax.JSON was
included in the application uber jar. I noticed that flink loads the application jar in a
child classloader. This is what most likely happened - 
> 1. WebHdfsFileSystem class was loaded through parent class loader since it is included
in flink-dist.jar.
> 2. WebHdfsFileSystem has reference to the org.mortbay.util.ajax.JSON but since it is
loaded through parent class loader, WebHdfsFileSystem can't read a class in child class loader.

> Ideally all the referenced classes should be available in the distribution jar so that
these sort of issues may not occur. 

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