A new logging experience!

I've been using logback for a few months now, and I'm impressed!

With excellent documentation and support, neat logging features, blazing performance and an innovating eclipse plugin, I've finally found a good replacement for the good old log4j.

The first thing I really appreciate compared to log4j or the java logging api is the documentation. The guide is well written, they have a nice demo, and you are up to speed in a few minutes.

Neat logging features

There are some very simple features which makes the life so much easier, such as the intelligent logger name reduction when it's too long: instead of simply truncating the name, it put the first letter of each package:

09:59:04.203 [main] INFO o.x.x.web.XoosentApplication - starting XooSent

The Mapped Diagnostic Context (MDC) is also a killing feature. It allows to associate metadata to the current thread, to correlate messages to their context. For instance in a web application with authentication, you can associate the user name to the the thread and add this user name to all log messages, without any change to your log calls. For instance, you add this at user authentication time:

MDC.put("user", username);

Then in your logback configuration you can use %Xuser in your pattern, and you will see the authenticated user name. It's that simple, and in multithreaded environment where multiple traces overlap, it really helps.
Updated: As Jorg pointed out, this isn't a feature introduced by logback, as log4j already supports NDC and MDC.

Performance

The parametrized logging is a key feature of logback, which improves performance by avoiding a toString() call when your message is not logged:

logger.debug("Hello, my name is {}, I am {} years old", username, age);

Note that obviously the performance gain applies only if you don't enclose your logging statements with if (logger.isDebugEnabled()) statements). But if you look at a benchmark run by Sebastien Pennec, one the developers of logback, it's really impressive:

Log4j direct debug call: 442
Log4j tested (isDebugEnabled) debug call: 19
Logback direct debug call: 435
Logback tested (isDebugEnabled) debug call: 10
Logback parametrized debug call: 15

OK, we all know how we should consider benchmarks, especially when written by someone biased as Sebastien obviously is, but these numbers can't be completly wrong, and what's interesting is that a logback parametrized call takes approximately the same time as a log4j isDebugEnabled call. Really cool!

Still on the performance area, logback introduces TurboFilters, which allows to filter logging before the logging event is actually constructed, saving a lot of unnecessary time.

Beyond console and files

Beyond classical ways to track and configure your logs, you have very interesting features with logback, such as a JMX configuration, and a new Eclipse plugin which is really neat.

One of the thing I like the most with this plugin is the option to go to the source which is at the origin of the log. Double click on the log, and it will open your source editor at the line where the log call is performed! Awesome! How many times did I use the search tool to find where a particular log call is performed in a big application, and waste time because the message was the result of a concatenation and thus my search failed...

Another interesting thing is the option to change the pattern and apply it to all the logs, including previous one.

And you have also a good filter option, where you can apply any logback filter expressions. This still need to be improved IMO to be able to apply the filter in real time to previous logs, but hey, it's only the first version of this plugin!

Excellent support

Last but not least the support is amazing. There isn't much traffic on the user mailing list for the moment (their documentation is so good :-)), but very often developers take time to answer your questions with a lot of details, trying to reproduce your environment, and providing whole configuration snippets. Great work, kudos to Sebastien, Jean-Noel and Ceki!