Adding a Routing Filter to log4j2

[mlangc]

Hi everyone, I created a small log4j2 extensions library, that features a routing filter that I find useful: https://github.com/mlangc/more-log4j2?tab=readme-ov-file#use-case-i-marker-based-log-throttling

What are your thoughts? Would it make sense to have such a filter in mainline log4j2?

[ppkarwasz]

Hi @mlangc,

Thank you for sharing this with us!

Would it make sense to have such a filter in mainline Log4j2?

It’s a bit early to say. At the moment, we only add plugins to the Log4j distribution once they have demonstrated long-term stability and are adopted by a broad user base. New plugins typically go through a “ramp-up” phase before reaching that point:

• They are listed on our website as third-party components, making them easier for users to discover and experiment with. For example, see my own Tomcat Lookup.
• If a component gains noticeable community interest, for instance, through downloads, GitHub stars, or feedback, we may consider integrating it into Log4j Core, which effectively means committing to maintaining it for the next decade or more.

Here’s what I’d suggest as next steps:

1. Publish your plugin on Maven Central, so that users can easily consume it.

2. Provide clear documentation, which you’ve already done a great job with.

3. Open a PR updating our Filters page to include:

   • A new “Third-party filters” section (below “Collection”) with a brief disclaimer explaining that these filters are not part of the official distribution (yet).
   • A short subsection about your filter, including a link to your documentation and repository.

This way, your work becomes visible to the community and can start building traction, which is exactly what we look for before considering inclusion in Log4j.

[mlangc]

Thanks a lot for the explanation and your suggestions.

more-log4j2 is already on Maven Central, however, the documentation only hints at that thanks to a Maven badge at the top. I'll improve on this a bit. I will also update the Why not extend log4j2 directly? section to reflect what you just wrote.

Please let me know if there is something else you'd like to see improved or adapted in more-log4j2 before you consider it ready to be linked in the Third-party filter section.

[mlangc]

PS: I've addressed the aforementioned points regarding the README in this commit already.

[ppkarwasz]

It looks good to me: please go ahead and open a PR to update our Filters page.

One small note: since a non neglible portion of users are still on Java 8, the baseline for Log4j 2.x remains Java 8. Your plugin’s requirement for Java 17 isn’t a blocker, but it may limit adoption among existing users.