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https://issues.apache.org/jira/browse/LOG4J2-1531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15429704#comment-15429704
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Roger Kapsi commented on LOG4J2-1531:
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I looked at {{@PluginElement}} et al. It's just a deferral to {{@Plugin}} and a
few other types that get their values again via {{addAttribute()}} which are
strings.
Please notice that I'm not looking for a replacement for attributes or
elements. The title of this ticket does say to change the value type of
attributes but that was before I dug deeper into the implementation of it. The
patch I submitted proposes a new {{add_ARG_ument(String, Object)}} method along
with a new {{@Plugin_ARG_ument}} annotation that doesn't interfere with
attributes or elements. It just allows plugin developers to pass arbitrary
objects into their {{@PluginFactory}}. The latter is desirable for programmatic
configuration. Be it plain Java or some other lang. I have mentioned Lamdas a
lot as they're as arbitrary as it gets but it applies equally well to other
objects. Either because they can't or it's simply not desirable.
Adding methods such as {{add(Appender)}} to the configuration builder works
(and you should probably do it) but it doesn't necessarily facilitate a
standard way of constructing things. Speaking in terms of a DSL it's not
necessarily something you want. You want a standard way of construction with
arbitrary arguments and you have a nice builder+plugin system for that. It's
only missing that one feature.
I have now solved the problem with a few hundred LoC of using a facade pattern,
inheritance and overriding some methods. It's sensitive to upstream changes but
it works. I wish it wasn't necessary though.
Please let me know when you've figured out the essence of this ticket. I'm
happy to iterate on it but attributes and elements aren't it and I don't want
to go in circles on it.
> Change attribute and component values from String to Object
> -----------------------------------------------------------
>
> Key: LOG4J2-1531
> URL: https://issues.apache.org/jira/browse/LOG4J2-1531
> Project: Log4j 2
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.6.2
> Reporter: Roger Kapsi
> Attachments: log4j2-1531-1.0.patch
>
>
> I was looking into creating a ConfigurationFactory/Builder that is backed by
> a Clojure DSL. It works rather beautifully until I tried to create a filter
> that is backed by a Clojure function. There is literally no way to pass
> arbitrary objects into a PluginFactory. All component values and attributes
> are assumed to be Strings.
> {code:java}
> (configuration
> (appender "stdout" "CONSOLE"
> (layout "PatternLayout"
> (attribute "pattern" "%d [%t] %-5level: %msg%n"))
> (filter "ClojureFilter"
> ;; This LoC doesn't work: addAttribute(key, value)
> ;; will store the toString() of the value. Bummer.
> ;; I'd the so easy and beautiful if it didn't.
> (attribute "fn" (fn [logger & more] (println logger)))))
>
> (logger "TestLogger" Level/INFO
> (appender-ref "rolling")
> (attribute "additivity" false))
> (root-logger Level/DEBUG
> (appender-ref "rolling")))
> {code}
> {code:java}
> @Plugin(name = "ClojureFilter", category = Node.CATEGORY, elementType =
> Filter.ELEMENT_TYPE, printObject = true)
> class ClojureFilter extends AbstractFilter {
> @PluginFactory
> public static ClojureFilter createFilter(
> @PluginAttribute("fn") IFn fn, ...) {
> return new ClojureFilter(fn, ...);
> }
> }
> {code}
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