log4j LogWrapper investigaion
Julius Davies
http://juliusdavies.ca/

August 2, 2006

Question:
------------------------
Does the LogWrapper.java I'm proposing work with different JVM's?  Can
it handle log4j.jar being unavailable no matter which JVM is being used?

Answer:
------------------------
Yes!

More JVM's need to be tested, but I think this is a pretty good starting
point.


Compiled with Sun 1.4.2_12*

                    no-log4j  yes-log4j
Linux
-------------------------------------------
Sun 1.3.1_18            x         x
Sun 1.4.2_12            x         x
Sun 1.5.0_07            x         x
Sun 1.6.0-beta2         x         x
JRockit 1.4.2_08        x         x
JRockit 1.5.0_06        x         x
Blackdown 1.4.2_03      x         x
IBM 1.4.2-SR4-1         x         x
IBM 1.5.0-J9-2.3        x         x

Windows
-------------------------------------------
Sun 1.4.2_05            x         x
Sun 1.5.0_07            x         x


*Note:  compiling with Sun 1.3.1_18 causes line 31 of Main.java
        to fail if log4j.jar is not present.

This is because Java 1.3's compiler creates bytecode that is more strict
with dependency checking.  The technique I'm proposing still works with a
Java 1.3 compiler, and even inspection via reflection of LogWrapper is fine.

Inspection (via reflection) of the underlying LogHelper (the situation
on line 31) is what fails at runtime if we use a "Java 1.3" _compiler_.
Inspection of LogHelper should usually fail, anyway, because LogHelper
is not a public class.

Thanks to Quy Nguyen for explaining the differences between javac 1.3 and
javac 1.4 to me.