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https://issues.apache.org/jira/browse/LOG4J2-1184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14980453#comment-14980453
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Robert Veitch commented on LOG4J2-1184:
---------------------------------------
I tried with 2.4.1 and get the same stack trace. I also notice that it depends
on which method I'm trying to log from. I can override and log from run()
without incident, but logging from addShutdownCallback() causes the NPE.
Adjusted sample class below:
public class CustomShutdownCallbackRegistry extends
DefaultShutdownCallbackRegistry {
private static Logger logger =
LogManager.getLogger(CustomShutdownCallbackRegistry.class);
public static void main(final String[] args) {}
@Override
public void run() {
logger.info("run msg");
super.run();
}
@Override
public Cancellable addShutdownCallback(final Runnable callback) {
// will throw NPE if uncommented
// logger.info("addShutdownCallback msg");
return super.addShutdownCallback(callback);
}
}
Finally, I do observe that if I make the logger an instance variable rather
than a static one, both log messages can complete successfully, which is
different from what I originally reported. This seems to indicate that the
custom callback registry object get initialized by the classloader at some
point prior to when the logging subsystem is ready, and prior to when the
actual instance is created?
> NullPointerException when attempting to configure logging in custom
> ShutdownCallbackRegistry
> --------------------------------------------------------------------------------------------
>
> Key: LOG4J2-1184
> URL: https://issues.apache.org/jira/browse/LOG4J2-1184
> Project: Log4j 2
> Issue Type: Bug
> Affects Versions: 2.2
> Environment: OSX, Ubuntu
> Reporter: Robert Veitch
> Priority: Minor
>
> I have a custom ShutdownCallbackRegistry implementation, which I've
> configured to be instantiated via:
> -Dlog4j.shutdownCallbackRegistry=<my_implementation>
> If I configure a logger in the normal way, either via a static or instance
> variable, I get a NullPointerException on startup. Something like:
> private static final Logger logger = LoggerFactory.getLogger(MyClass.class);
> I think this is probably because the configured registry instance gets
> created prior to the log4j subsystem responsible for loggers. My workaround
> is to define the logger variable without assigning it:
> private static final Logger logger;
> And then assigning it as the first line of my run method:
> public void run() {
> logger = LoggerFactory.getLogger(MyClass.class);
> // shutdown registry code
> }
> But if possible, it seems like the instantiation order should be reworked so
> that implementers of a custom registry do not have to do this.
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