Qinghui Xu created HADOOP-15639:
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Summary: Classloader issue with hadoop cmd -libjars option
Key: HADOOP-15639
URL: https://issues.apache.org/jira/browse/HADOOP-15639
Project: Hadoop Common
Issue Type: Bug
Reporter: Qinghui Xu
'-libjars' option gives the possibility to add extra libraries in a hadoop
command by providing a custom URLClassLoader to fetch jars regarding to the
option.
The classloader is provided to both hadoop Configuration and the main thread's
context classloader, so that when calling Configuration#getClass or using
Class.forName the class can be loaded by the URLClassLoader.
But two instances of URLClassLoader are provided to Configuration and to thread
context classloader respectively, which makes a same class possible to be
loaded twice by two classloaders. And class loaded by different classloaders is
considered different.
So the following assertion will fail:
{code:java}
// CustomFileSystem is provided by -libjars option
Class<?> clazz1 = conf.getClass("CustomFileSystem");
Class<?> clazz2 = Class.forName("CustomFileSystem");
// The two classes are different
assert clazz1 == clazz2{code}
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