[jira] [Created] (FLINK-3271) Using webhdfs in a flink topology throws classnotfound exception

["Abhishek Agarwal (JIRA)" <ji...@apache.org>]

Abhishek Agarwal created FLINK-3271:
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             Summary: 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


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 is included in the 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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