Advantage of log4j

Question

What\'s the advantage of log4j over set System.out and System.err to output to a log file?

Answer 1

Actually, you should look into the slf4j facade these days, as it allows you to use {}-placeholders for the most concise statements. You can then use the appropriate logging framework behind slf4j to handle the actual treatment of your log statements. This could be log4j or the slf4j-simple which just prints out all of INFO, WARN and ERROR, and discards the rest.

The crucial observation you need to make is that the WRITING of log statements is done when the code is written, and the DECISION of what is needed is done when the code is deployed, which may be years after the code was written and tested. System.out.println requires you to physically change your code to get rid of them, which is unacceptable in a rigid write-test-deploy cycle. IF the code changes, it must be retested. With slf4j you just enable those you want to see.

We have full logging in the test phase, and rather verbose logging in the initial period of a production deployment, after which we go down to information only. This gives us full information in a scenario where debugging a case is very rarely possible.

You might find this article I wrote interesting. The target audience is beginning Java programmers, with my intention of giving them good habits from the start. http://runjva.appspot.com/logging101/index.html