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From jason hadoop <jason.had...@gmail.com>
Subject Re: JNI and calling Hadoop jar files
Date Tue, 24 Mar 2009 10:52:50 GMT
The exception reference to *org.apache.hadoop.hdfs.DistributedFileSystem*,
implies strongly that a hadoop-default.xml file, or at least a  job.xml file
is present.
Since hadoop-default.xml is bundled into the hadoop-0.X.Y-core.jar, the
assumption is that the core jar is available.
The class not found exception, the implication is that the
hadoop-0.X.Y-core.jar is not available to jni.

Given the above constraints, the two likely possibilities are that the -core
jar is unavailable or damaged, or that somehow the classloader being used
does not have access to the -core  jar.

A possible reason for the jar not being available is that the application is
running on a different machine, or as a different user and the jar is not
actually present or perhaps readable in the expected location.

Which way is your JNI, java application calling into a native shared
library, or a native application calling into a jvm that it instantiates via
libjvm calls?

Could you dump the classpath that is in effect before your failing jni call?
System.getProperty( "java.class.path"), and for that matter,
"java.library.path", or getenv("CLASSPATH)
and provide an ls -l of the core.jar from the class path, run as the user
that owns the process, on the machine that the process is running on.

<!-- from hadoop-default.xml -->
  <description>The FileSystem for hdfs: uris.</description>

On Mon, Mar 23, 2009 at 9:47 PM, Jeff Eastman <jdog@windwardsolutions.com>wrote:

> This looks somewhat similar to my Subtle Classloader Issue from yesterday.
> I'll be watching this thread too.
> Jeff
> Saptarshi Guha wrote:
>> Hello,
>> I'm using some JNI interfaces, via a R. My classpath contains all the
>> jar files in $HADOOP_HOME and $HADOOP_HOME/lib
>> My class is
>>    public SeqKeyList() throws Exception {
>>        config = new  org.apache.hadoop.conf.Configuration();
>>        config.addResource(new Path(System.getenv("HADOOP_CONF_DIR")
>>                                    +"/hadoop-default.xml"));
>>        config.addResource(new Path(System.getenv("HADOOP_CONF_DIR")
>>                                    +"/hadoop-site.xml"));
>>        System.out.println("C="+config);
>>        filesystem = FileSystem.get(config);
>>        System.out.println("C="+config+"F=" +filesystem);
>>        System.out.println(filesystem.getUri().getScheme());
>>    }
>> I am using a distributed filesystem
>> (org.apache.hadoop.hdfs.DistributedFileSystem for fs.hdfs.impl).
>> When run from the command line and this class is created everything works
>> fine
>> When called using jni I get
>>  java.lang.ClassNotFoundException:
>> org.apache.hadoop.hdfs.DistributedFileSystem
>> Is this a jni issue? How can it work from the commandline using the
>> same classpath, yet throw this is exception when run via JNI?
>> Saptarshi Guha

Alpha Chapters of my book on Hadoop are available

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