The benefits and downsides of using Apache Commons Logging already has been discussed endlessly on the web, but last Thursday I've encountered a really nasty problem which imo finally nails it as unsuited for usage with portals.
The problem is commons-logging using the ContextClassLoader to determine the current LogFactory and logger.
As a Portal/PortletContainer (e.g. pluto-container) depend on cross-context invocation, determining the LogFactory for a portal/portletcontainer class while being cross-context invoked from a portlet application,
this means commons-logging will use the invoking portlet application its classloader instead of the expected/needed classloader of the portal/portletcontainer...
Now, this could be "fixed" by either wrapping each and every cross-context callback into the portal/portletcontainer and temporarily setting the current ContextClassLoader or wrapping commons-logging itself,
but imo the LogFactory "resolving" solution applied by commons-logging is fundamentally problematic for our purpose.
I won't go as far as saying commons-logging is bad and should never be used, but for portals/portletcontainers and cross-context application handling it just doesn't fit.
Now, where does that leave us?
Looking at alternatives, I think there are only a few:
a) only using Java(4) logging
b) using Apache Log4J directly
c) switch to slf4j (http://www.slf4j.org)
Of the above options, a and b forces end users (integrators) of Pluto to leverage the same logging solution which imo is too restricted:
- Java logging is too limited and a nuisance to use (personal opinion)
- Log4J is great but not everyone enjoys it, and for instance Logback (LGPL) is building up a lot of users because of its (supposedly) higher performance and lesser overhead
AFAIK, that leaves only slf4j which, although not ASF based, has a compatible license and is being adopted already a lot by other ASF projects.
The benefit of slf4j is also (besides "fixing" the commons-loggings problems) that it supports gradual "migration" from commons-logging through its jcl-over-slf4j solution.
During this weekend, I've spend some time doing a local migration of both Pluto 2.0 and Jetspeed-2.2 to slf4j to see how much trouble that would be and if I would encounter unexpected problems.
I can now attest that this migration is mostly "painless", slf4j even has a migrator tool which does most of the hard work (code wise).
Of course, there was some "pain" in the maven dependencies migration but I could complete that in a reasonably short time (manually) as well.
After all this, the JSR-286 TCK (of course) still completed successfully and logging still works just as fine.
As I see no real alternative for solving this imo blocking issue, I think finalizing this migration to sfl4j is the only reasonable resolution.
I'll also send a message to the Pluto dev list soliciting further feedback on this, but if nobody objects I intend to commit my changes for this soon (I will create a separate issue for migrating Jetspeed-2.2 to slf4j).