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https://issues.apache.org/jira/browse/LOG4J2-3640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17645409#comment-17645409
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Ralph Goers commented on LOG4J2-3640:
-------------------------------------
I found a couple of problems.
# Your Log4j2 plugin is not created with the annotation processor so no
Log4j2Plugins.dat file is created. We don't ever recommend this as using class
path scanning via the packages element in the configuration is slow. I suspect
we may have removed support for package scanning in 3.0.
# You also didn't use the annotation processor for your 3.0 plugins. That is
required.
# You add --adds in the log4j3 test pom. But Maven isn't treating that as a
JPMS module so that fails. I added a module-info.java file instead.
I've created a pull request to your repo with the changes I made to get it
working.
> @Plugin not compatible between 2.x and 3.x
> ------------------------------------------
>
> Key: LOG4J2-3640
> URL: https://issues.apache.org/jira/browse/LOG4J2-3640
> Project: Log4j 2
> Issue Type: Bug
> Components: Plugins
> Affects Versions: 3.0.0
> Reporter: Rob Spoor
> Priority: Major
>
> I had an issue with resolving Log4j2 2.19.0 as a module. While I resolved the
> issue by adding an explicit {{--add-opens}} clause, I still found something
> that appears to be an issue.
> According to [this
> comment|https://stackoverflow.com/questions/74592131/maven-log4j-class-not-found#comment131670094_74592131]
> from [~rgoers], {quote}Plugins should NOT need to be recompiled
> {quote}
> Because of an earlier comment on my question I had tried to use version
> 3.0.0-SNAPSHOT. That produced some compiler errors. While some were easy
> enough to solve to be compatible with versions 2.19.0 and 3.0.0-SNAPSHOT, the
> moved {{@Plugin}} annotation meant I couldn't compile my project for both
> versions 2.19.0 and 3.0.0-SNAPSHOT. That made me believe that plugins written
> for 2.19.0 are *not* compatible with 3.0.0.
> I have created a little POC: [https://github.com/robtimus/log4j-compat-test].
> This consists of 3 Maven modules:
> * A module with only a simple plugin
> * A module to test this plugin in Log4j2 2.19.0
> * A module to test this plugin in Log4j2 3.0.0-SNAPSHOT
> The entire project can be tested using {{mvn test}}. Right now this fails
> because, as expected, the moving of the {{@Plugin}} annotation caused the
> plugin to *not* be resolved.
> I've also included a "legacy" plugin class in the 3.0.0-SNAPSHOT test module
> that shows that the deprecated annotations
> {{org.apache.logging.log4j.core.config.plugins.PluginAttribute}} and
> {{org.apache.logging.log4j.core.config.plugins.PluginFactory}} still work;
> it's the (forced) replacement of
> {{org.apache.logging.log4j.core.config.plugins.Plugin}} with both
> {{org.apache.logging.log4j.plugins.Plugin}} and
> {{org.apache.logging.log4j.plugins.Configurable}} that causes the plugin
> written for version 2.19.0 to not work.
> ----
> I think that the following should be done, to prevent forcing people rewrite
> all of their existing plugins:
> * Re-adding the {{org.apache.logging.log4j.core.config.plugins.Plugin}}
> annotation, but make it deprecated.
> * The plugin registration code should treat this plugin as a combination of
> {{org.apache.logging.log4j.plugins.Plugin}} and
> {{{}org.apache.logging.log4j.plugins.Configurable{}}}. There may be another
> one, for the {{category}} attribute of the old annotation, but I couldn't
> find out which one yet.
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