Android and Log4j

[Ralph Goers]

Log4j added support for Java 9 by:
Converting the Log4j-API jar to a multi-release jar that includes support for StackWalker and the new Process Id support.
Adding a module-info.jar to the Log4j API jar.

We are now getting complaints from Android users (as well as a few others) that their tools no longer work with log4j. During development I ran into problems with OSGi. The problems seem to mostly revolve around the fact that they can’t deal with the classes for Java 9. I was surprised that Android is failing on the classes in META-INF/versions/9 as I had assumed that would be an invalid location for a class file prior to Java 9, but that seems not to be the case. The fact that module-info.java turns into a class file also seems to be a problem since the various tools are seeing it and having problems with it.

We have been discussing various ways to handle this in https://issues.apache.org/jira/browse/LOG4J2-2133 <https://issues.apache.org/jira/browse/LOG4J2-2133>. There seems to be a strong push to just remove the support for Java 9 since it is breaking so many things.

It seems impossible to have a module-info.java file in a jar that is going to be included in Android. If this had been a json file that was interpreted by the classloader or had a different file extension other than .class we wouldn’t be in this mess. We also need another mechanism to bring in our code that uses StackWalker as calling it via Reflection and emulating lambda expressions seems like it would be painful and slow.

Do you have any recommendations on how we can resolve this impasse? 

Ralph