Alex Rivera | Logout

log4j vs. System.out.println - logger advantages?

Asked 2010-04-28T07:24:41.757
27

I'm using log4j for the first time in a project. A fellow programmer told me that using System.out.println is considered a bad style and that log4j is something like standard for logging matters nowadays.

We do lots of JUnit testing - System.out stuff turns out to be harder to test.

Therefore I began utilizing log4j for a Console controller class, that's just handling command-line parameters.

// log4j logger config 
org.apache.log4j.BasicConfigurator.configure();
Logger logger = LoggerFactory.getLogger(Console.class);
Category cat = Category.getRoot();

Seems to work: 

logger.debug("String");

Produces:

1 [main] DEBUG project.prototype.controller.Console  - String

I got two questions regarding this:

  1. From my basic understanding using this logger should provide me comfortable options to write a logfile with timestamps - instead of spamming the console - if debug mode is enabled at the logger?
  2. Why is System.out.println harder to test? I searched stackoverflow and found a testing recipe. So I wonder what kind of advantage I really get by using log4j.
java logging junit timestamp logfiles
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1 Answer

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Anything that you print to System.out will go to "standard out", and while you can redirect standard out to a file and compare it, what have you, that is very inflexible. Additionally, you cannot filter what goes to standard out if you use System.out... everything will be printed. With log4j, you can set different logging levels, so that logging messages that are below a certain severity/importance threshold are not printed (e.g. if you change the logging level to WARN, then DEBUG and INFO messages will not be displayed anymore).

Additionally, log4j allows logging to be controlled on a class-by-class basis, whereas System.out can only be controlled at the granularity of the entire application (if you redirect System.out, you redirect it for the entire program). By contrast, each logger in log4j can be given a different appender. In addition, you can give a log4j logger multiple appenders (so that it goes the system logger, and over the network, for example). You can even have a log4j logger append to a StringBuilder, so that you can easily read what was written. And while System.out can be redirected, this redirection tends to be fairly limited; System.out can be redirected to a file or to a pipe (to another program), but you wouldn't be able to redirect it to a URL, for example; by contrast, it would be very easy to create an appender that transmits logging messages using HTTP POST.

answered 2010-04-28T07:33:26.147

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