Logging in POI is used only as a debugging mechanism, not a normal runtime logging system. Logging is ONLY for autopsie type debugging, and should NEVER be enabled on a production system. Enabling logging will reduce performance by at least a factor of 100. If you are not developing POI or trying to debug why POI isn't reading a file correctly, then DO NOT enable logging. You've been warned.
Hence, we need to be able to easily disable it entirely and make POI not dependent on any logging package.
Every class uses a POILogger
to log, and gets it using a static method
of the POILogFactory
.
The POILogFactory
uses the NullLogger
by default;
it can be instructed to use any other POILogger
implementation
by setting the system property org.apache.poi.util.POILogger
.
Each class in POI can get its POILogger
by calling a static method
of the POILogFactory
.
Each class in POI can log using a POILogger
, which is an abstract class.
We decided to make our own logging facade because:
There are three implementations available, and you can roll out your own, just
extend org.apache.poi.util.POILogger
.
Discards every logging request.
Sends every logging request to System.out.
Sends every logging request to the Commons Logging package. This can use JDK1.4 logging, log4j, logkit, and is an actively maintained Jakarta Project.