While looking into a production issue, I recently uncovered the following inconsistency.

In log4j.properties, if you declare a logger twice:

log4j.rootCategory=FATAL, console

log4j.logger.ReproduceLog4jProblem=INFO,console
log4j.logger.ReproduceLog4jProblem=INFO,console

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%p [(%c{3})] %m%n

There is no warning or strange behavior.  If you declare a logger and a category (in either order) with the same name like this:

log4j.rootCategory=FATAL, console

log4j.category.ReproduceLog4jProblem=INFO,console
log4j.logger.ReproduceLog4jProblem=INFO,console

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%p [(%c{3})] %m%n

Then when you try to write to that log, the following error appears:

log4j:ERROR Attempted to append to closed appender named [console].

I understand that this is really a configuration error, but I believe that the behavior should be the same in either case.  But maybe an improvement would be to display a warning when redefining any loggers or categories.  Failing either of those, is there a way to show a better error rather than closed appender?  Googling for that error message did not show anything related to duplicate mixed logger and category configuration.


FYI this is the simple class I used to test this:

public class ReproduceLog4jProblem {

	private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger
			.getLogger(ReproduceLog4jProblem.class);
	
	public static void main(String[] args) {
		LOG.info("Log!");
	}

}