Question

I am thinking off migrating a java 1.4.2 project from log4j to slf4j. It is the advantage of parameterised logging and the code clarity (no need if log.isdebug..) That is drawing me to such considerations.

Are there performance overheads of converting to slf4j?

Last time I checked if I could use logback, it has a requirement on the jdk which mandates it to be att least 1.5 which is why I am considering slf4j and log4j.

Answer 1

No, you should get a performance advantage from slf4j if anything, because (if you use parameterized messages) then slf4j defers turning its parameters to strings until it has checked that the message won’t be filtered out by log level:

There exists a very convenient alternative based on message formats. Assuming entry is an object, you can write:

Object entry = new SomeObject();
logger.debug("The entry is {}.", entry);

After evaluating whether to log or not, and only if the decision is affirmative, will the logger implementation format the message and replace the ‘{}’ pair with the string value of entry. In other words, this form does not incur the cost of parameter construction in case the log statement is disabled.

The following two lines will yield the exact same output. However, the second form will outperform the first form by a factor of at least 30, in case of a disabled logging statement.

logger.debug("The new entry is "+entry+".");
logger.debug("The new entry is {}.", entry);