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https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14562034#comment-14562034
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Guozhang Wang commented on MAPREDUCE-1700:
------------------------------------------
More specifically, I feel for it to really work, one has to do sth. like:
{code}
Thread thread = Thread.currentThread();
ClassLoader old = thread.getContextClassLoader();
thread.setContextClassLoader(newClassLoader);
try {
// user code like process(), map(), reduce(), etc..
} finally {
thread.setContextClassLoader(old);
}
{code}
> User supplied dependencies may conflict with MapReduce system JARs
> ------------------------------------------------------------------
>
> Key: MAPREDUCE-1700
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1700
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: task
> Reporter: Tom White
> Assignee: Tom White
> Fix For: 2.0.3-alpha
>
> Attachments: MAPREDUCE-1700-ccl.patch, MAPREDUCE-1700-ccl.patch,
> MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, MAPREDUCE-1700.patch,
> MAPREDUCE-1700.patch, MAPREDUCE-1700.patch, MAPREDUCE-1700.patch,
> MAPREDUCE-1700.patch, MAPREDUCE-1700.patch
>
>
> If user code has a dependency on a version of a JAR that is different to the
> one that happens to be used by Hadoop, then it may not work correctly. This
> happened with user code using a different version of Avro, as reported
> [here|https://issues.apache.org/jira/browse/AVRO-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852081#action_12852081].
> The problem is analogous to the one that application servers have with WAR
> loading. Using a specialized classloader in the Child JVM is probably the way
> to solve this.
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