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https://issues.apache.org/jira/browse/LOG4J2-100?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480800#comment-13480800
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Ralph Goers commented on LOG4J2-100:
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After looking at the patch and thinking about this I'm leaning away from
allowing the LogEvent to be extended for two reasons.
1. As you point out MapRewritePolicy will have a problem rewriting any event
that isn't a Log4jLogEvent. Currently MapRewritePolicy is the only
RewritePolicy but this problem will occur with any RewritePolicy.
2. Having multiple variations of LogEvents will cause problems for applications
that accept serialized LogEvents as they will need to have the various classes
needed to deserialize the events. This is an area I would really like Joern's
and Scott's feedback on as they have been dealing with Lillith and Chainsaw and
presumably understand the issues better than me.
Even adding a new field that allows arbitrary serializable objects to be added
to the event could have the same impact as item 2, so before anything is done
with this I would really like to get more feedback.
> Allow Log4jLogEvent serialization with subclasses
> -------------------------------------------------
>
> Key: LOG4J2-100
> URL: https://issues.apache.org/jira/browse/LOG4J2-100
> Project: Log4j 2
> Issue Type: Improvement
> Components: Appenders, Core
> Affects Versions: 2.0-beta2
> Reporter: Das Archive
> Priority: Minor
> Labels: patch
> Attachments: allow_log_event_subclass_serialization.patch,
> ClassChangingAppender.java
>
>
> Hello!
> I am working on an extension which requires adding content to log events. As
> the method of adding it to the mdc has quite some overhead and the data I
> want to add is not really context-related, I was looking for an alternative
> and thought about subclassing Log4jLogEvent.
> But as AsynchAppender uses the Log4jLogEvent serialize/deserialize methods
> this didn't work.
> So I extended the serialize/deserialize methods to also work with subclasses.
> I'll quickly explain the the changes in the patch (in order):
> Log4jLogEvent.java:
> - not related to the improvement: ndc is never written
> - added a clone constructor to allow easy creation of subclasses Events based
> on Log4jLogEvents
> - make "serialize" a dynamic method as we always have an Event to serialize
> and it allows overwriting the method in subclasses
> - make use of the existing "readResolve" method instead of rinventing the weel
> - LogEventProxy private -> protected to allow subclassing this inner class in
> subclasses
> - change all instance field from private to protected to make life easier in
> subclasses
> - I didn't see a reason why "readResolve" should return an Object instead of
> "Log4jLogEvent"
> AsynchAppender.java:
> - this is actually the only change necessary to make the changes work with
> the existing code-base
> The only instance where subclassing still doesn't work (i.e. the subclass is
> removed) is in the MapRewritePolicy, but I don't think this will be a big
> issue and apart from adding a function to allow changing the Map in
> Log4jLogEvent I couldn't think of a way to solve this.
> Please note, that I haven't had the time to actually test the modified code
> yet!
> Best Regards,
> Das
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