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javalog4j

Is Log4j isDebugEnabled() necessary before using logger.debug()?

When I was going through some code, I noticed the use of logger as follows, 

if(logger.isDebugEnabled())   
    logger.debug("Something..");

But in some codes, I observed like this.

logger.debug("Something..");

When I looked at the source of log4j, in the debug() method of Logger itself if(logger.isDebugEnabled()) was checked. Then why do we need this unnecessary overhead if(logger.isDebugEnabled())??

Solution

  • It's useful when the String your passing to logger.debug(...) takes time to evaluate, in that case you can skip this evaluation if debug is not enabled.

    if(logger.isDebugEnabled()) {
    logger.debug("The meaning of life is " + calculateMeaningOfLife());
}

    IMO this makes the code a lot less readable so it should only be used when there's a significant performance improvement.

    Edit 10 years after the original answer:

    Now that we have lambdas, loggers have added support for suppliers that are only called when necessary. So the above code could be simplified to:

        logger.debug("The meaning of life is {}", () -> calculateMeaningOfLife());

    And the logger will only call calculateMeaningOfLife() if the message should be logged.