Why use an extra if condition for logger.debug()? [duplicate]

Question

Possible Duplicate:
In log4j, does checking isDebugEnabled before logging improve performance?

I have seen people using log4j in the manner below:

if(logger.isDebugEnabled())
{
    logger.debug(" message ");
}

However, I checked the documentation for the logger.debug API and found that it checks if debug is enabled before logging the message. In that case, what is the point of writing extra the if?

Wouldn't it be exactly the same to just write

logger.debug(" message ");

?

Answer 1

If you're really just writing

logger.debug(" message ");

then there's no benefit. But consider:

logger.debug("This: " + message + " happened on thread " + thread +
            "because " + cause);

You don't want that string concatenation (and more expensive conversions, potentially - think about things that you might want to log, but which are costly to convert to strings) to be executed if the result is just going to be thrown away.

If logging has a significant performance impact in the normal case, that's a disincentive to add logging code which could really help you in situations where suddenly you want to turn diagnostics on.

Answer 2

I think the idea here is to prevent any parameter evaluation - in your case it's simple, but for example let's say it was more like:

logger.debug("Foo" + bar() + " bar: " + foo());

Okay this is contrived, but if debug is not enabled, you may not want to execute bar() and foo() and the string concatenation...