I’ve been going through my old code, looking for stuff that might be worth sharing. At the same time, I’ve been maven-izing my builds, and decided I should revisit each dependency, as some of this code is so old the dependencies are very out of date and/or included in the JDK now. Which brings me to log4j.
I’ve literally used log4j on everything I can ever remember doing in Java, but not anymore. Don’t get me wrong, I have no problem with it, and may continue to use it in my applications (if I don’t like logback), but I won’t be including it in any libraries anymore. After 8 years, I’ve finally adopted JUL. Here’s the options and why I chose JUL:
JUL (java.util.logging)
Pros
I’ll start with the victor, because the reason is the simplest. No dependency or version issues, one less thing to download, guaranteed to be there. There is also plenty of code out there to use one of the other frameworks to do your actual logging, so the config isn’t really a burden on the developers using the library.
Cons
Not sure yet. It’s not widely used, but I think that’s because there are far more Java frameworks/applications out there than libraries. There is also a performance issue with SLF4J when you have JUL logging set to a low level, but you shouldn’t need to run (presumably stable) libraries in debug or trace when performance is an issue (e.g. in production), only when you’re trying to debug something. The JUL’s actually logging isn’t really relevant here, as I think most applications will just be running it’s output through their own logging framework.
log4j
Pros
Works great, very stable, hasn’t changed in long enough that you only have version issues when you’re dealing with REALLY old code.
Cons
Less people are using it, more projects are going to SLF4J/Logback. These new frameworks do add some nice features, and log4j is basically abandoned, so I think it’s time to stop doing anything new with it.
commons logging
Pros
None?
Cons
I’ve always been against commons logging, because 99% of the time, it was just used to wrap log4j. The logic was that you could plug custom logging into it, but you can do that with log4j already, so it’s basically an abstraction of an extensible framework, with zero added value. Actually you have less value because you lose things like MDC. At this point it’s like a virus that just won’t go away, and always seems to end up in the classpath somehow. As far as I’m concerned, I consider this a completely superseded library.
logback
Pros
From what I can gather, logback really is (as claimed on their website) the continuation of log4j. Not having used it, I can only assume this is a good thing, and it just adds new features like parameterization. I’m going to try logback in my next application, and since logback includes slf4j, I will access my library logging that way.
Cons
It’s not really in wide usage yet, which means that a library requiring it is going to add an extra dependency.
slf4j
Pros
If logback is the modern version of log4j, slf4j is the supposedly useful version of commons logging, and supposedly improved version of JUL. It’s not a logger per se, it’s just an API/facade. It has the ability to combine multiple logging APIs and legacy frameworks into one stream, which is why it seems to be getting traction on complex applications.
Cons
I’ve had some serious versioning issues with slf4j, due to some methods being removed or changed, so you end up with older code throwing errors when you use a newer version, thus requiring that you only use the old version and introduce the chance for strange errors in code expecting the newer version. For this reason, I don’t feel very comfortable specifying any version of slf4j, and I will leave it to the user to add it if they wish.
Conclusion
So JUL seems like the best choice for a stable, single-purpose library to use, as it’s the least imposing on whatever uses it. It should be noted that I haven’t actually used JUL yet in a real app, so perhaps I will find out that there’s an actual reason for its lack of popularity. If that’s the case, I will likely use slf4j, and try and find out which methods cause issues so I can avoid them, and not be the person someone else curses for requiring it.