Hi,
I have a question that is probably related to SPARK-1870
<https://issues.apache.org/jira/browse/SPARK-1870>. Basically I have also
encountered the issue that with separate classloaders while developing a
programming framework where I have to use reflection inside the application
code.
To simply the question, let's say my framework code depends on a jar with
an older version and the application code depends on the same jar with a
newer version. And let's say that jar has a class named CommonClass. I used
a customized post-delegation class loader so that these two version can
exist separately into separate class loader. And if I do sth. like:
public static void main(String arg[]) throws Exception {
// Say this is framework code
new CommonClass().printJarVersion();
// Set the customized class loader as thread context class loader
Thread thread = Thread.currentThread();
ClassLoader oldClassLoader = thread.getContextClassLoader();
File appJar = new File("/dir/to/app/class/path");
URL[] classpath = new URL[] { appJar.toURI().toURL() };
PostDelegationClassLoader newClassLoader = new
PostDelegationClassLoader(classpath);
thread.setContextClassLoader(newClassLoader);
try {
// Say this is application code, like process().
new CommonClass().printJarVersion();
thread.getContextClassLoader().loadClass("CommonClass").newInstance().printJarVersion();
} finally {
thread.setContextClassLoader(oldClassLoader);
}
}
-----------------------
It will print:
CommonClass: version 1
CommonClass: version 1
CommonClass: version 2
As one can see I have to use reflection to explicitly specify the
customized class loader if I want to create the class with the new version.
This is definitely bad for the users.
I saw there are some discussions around this issue on SPARK-1870, but not
so sure what is the final solution to this. Anyone could help me out?
-- Guozhang
