Log4j: Change log level programmatically that works for to-be created loggers

Question

I declare loggers in my code like this:

Logger logger = LoggerFactory.getLogger(MyClass.class);

I would like to be able to change the log level of my loggers programmatically at runtime. I have tried iterating over the loggers in the repository via the LogManager, but it only applies the new log level to loggers that are instantiated in the code. If a new logger instance is created, it does not use the new log level. My requirement is such that the log level in my web application needs to be configurable via an Administrative GUI, and this new log level needs to apply to all loggers in my code (exclude third party library logging, e.g. JSF, Spring, Hibernate etc).

This is what I'm doing now which does not meet my requirements as it does not apply the log level to newly instantiated loggers:

Enumeration<Logger> currentLoggers = LogManager.getCurrentLoggers();
while(currentLoggers.hasMoreElements()) {
    Logger logger = currentLoggers.nextElement();
    if (StringUtils.startsWith(logger.getName(), "com.my.company")) {
        logger.setLevel(logLevel);
    }
}

I am using Log4j 1.2.17.

Answer 1

Didn't find the resource anymore, but as to my faded memory LogManager.getLogger("com.my.company").setLevel(whateverloglevel) should do the job.

All loggers that are created with LogManager.getLogger(MyClass.class) where MyClass is in com.my.company or in a subtree of that will be affected.

whateverloglevel is one of Level:

ALL

    The ALL has the lowest possible rank and is intended to turn on all logging.

DEBUG

    The DEBUG Level designates fine-grained informational events that are most useful to debug an application.

ERROR

    The ERROR level designates error events that might still allow the application to continue running.

FATAL

    The FATAL level designates very severe error events that will presumably lead the application to abort.

INFO

    The INFO level designates informational messages that highlight the progress of the application at coarse-grained level.

OFF

    The OFF has the highest possible rank and is intended to turn off logging.

TRACE

    The TRACE Level designates finer-grained informational events than the DEBUG

WARN

    The WARN level designates potentially harmful situations.

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Be aware that this probably does not work in log4j 2.

For (I think) version >= 2.4 see:

• log4j FAQ
• Programmatically change log level in Log4j2