We do need better docs on this. 3.0 is going to be a mixed bag. It will be easier for “normal” applications because plugins now use ServiceLoader instead of the Log4jPlugins.dat file. However, it is going to be more challenging for those developing plugins if they use the Java Platform Module System.
As one might imagine, the compiler now has a modulePath in addition to a classPath. When no module-info.java is present Maven will set things up to only use the classPath, which will work as normal. However, when a module-info.java file is present than Maven will configure the project and its tests to use the modulePath. By itself this isn’t a problem. However, the Java compiler ONLY looks for Annotation processors automatically on the classPath. This means anyone using JPMS while compiling plugins will have to explicitly configure the annotation processor. There is a second issue when using JPMS. While our annotation processor generates the service class and service definition file, JPMS requires that the Log4jPlugins service class must be declared in module-info.java. This is somewhat of a problem because the compiler will fail if it finds the module-info.java references the Log4jPlugins service class because the annotation processor hasn’t generated it yet. The only recourse to this is to do a proc=only compile that does not include the module-info.java class followed by a full compile with proc=none. Personally, I think this is a but in javac but I suspect it would be a major change to fix it. I have meant to write a blog post on all of this basically to ask the question, “Is JPMS really worth it”? Ralph > On May 29, 2021, at 11:06 AM, Matt Sicker <boa...@gmail.com> wrote: > > Hey all, that itch is back to figure out how to complete my previous > attempt at the plugin system updates (started a little over a year ago > and put on pause at some point). I'm currently working on getting that > branch back up to working again with master (mostly needing to update > module-info files), and I'm hoping to map out and figure out the path > forward on completing it. > > With that being said, one major aspect of this project will be > explaining how the 2.x plugin system works, how it relates to the 3.x > system, and the gist of how I'd like to restructure things. Does > anyone here have any preferences on how I share some docs about this? > I could record some videos that go over code and such, or I could > write things up blog style. Note that these docs would be focused at > fellow log4j developers and not necessarily the user manual. I still > plan to have proper API docs and manual pages for the system, but > those would be targeted for users writing their own extensions mainly. > > Link for background info: > https://issues.apache.org/jira/browse/LOG4J2-2803 >
