I haven’t looked at your code but when you create the “real” appender you need 
to change its name to match the name of the selector so that AppenderRefs work.


> On Sep 18, 2016, at 9:24 PM, Gary Gregory <garydgreg...@gmail.com> wrote:
> I've implemented a first cut in the branch LOG4J2-1597 but I think I need 
> some help to connect the final dot (or two).
> When I run the new unit test 
> org.apache.logging.log4j.core.appender.ScriptSelectorAppenderTest, the status 
> logger shows:
> 2016-09-18 21:19:09,393 main ERROR Unable to locate appender "SelectIt" for 
> logger config "root"
> 2016-09-18 21:19:09,465 main ERROR Unable to locate appender "SelectIt" for 
> logger config "root"
> 2016-09-18 21:19:09,485 main ERROR Unable to locate appender "SelectIt" for 
> logger config "root"
> 2016-09-18 21:19:09,505 main ERROR Unable to locate appender "SelectIt" for 
> logger config "root"
> Which initially makes sense: the appender created and returned by the builder 
> of "SelectIt" is really an appender named "List2".
> I tried to add a hack in 
> org.apache.logging.log4j.core.appender.ScriptSelector.Builder.build() to no 
> avail:
>             // This feels like a hack and it does not work:
>             configuration.getAppenders().put(name, appender);
> Any thoughts?
> Gary
> On Sat, Sep 17, 2016 at 9:48 AM, Ralph Goers <ralph.go...@dslextreme.com 
> <mailto:ralph.go...@dslextreme.com>> wrote:
> See inline
>> On Sep 16, 2016, at 10:31 PM, Gary Gregory <garydgreg...@gmail.com 
>> <mailto:garydgreg...@gmail.com>> wrote:
>> On Fri, Sep 16, 2016 at 8:38 PM, Ralph Goers <ralph.go...@dslextreme.com 
>> <mailto:ralph.go...@dslextreme.com>> wrote:
>> Gary,
>> I have no problem with components that can be dumbed down to do simple 
>> things. I do have a problem with components that only do simple things 
>> because people will constantly asked to have them be enhanced.
>> As for what you are proposing here, can I just say “No”?  
>> Sure! :-) You can say whatever you want! :-) 
>> Having the Appenders element deferred just smells to me and having an 
>> arbitrary script there just seems weird to me. Does it even have a contract 
>> or is it a free-for-all? How does it cause multiple appenders to be 
>> initialized? 
>> I think the RoutingAppender is a more appropriate solution. However, if you 
>> want to dumb it down a bit and turn it into an AppenderSelector I’d be ok 
>> with that. However, it would still be fairly similar to the RoutingAppender.
>> OK, so going back to one of your eariler messages:
>> ==copy start==
>> This sort of sounds like you want an Appender Selector, which would be an 
>> Appender that uses a Selector to figure out which Appender to delegate to. 
>> This is a bit like the PatternSelector. I would imagine it would make sense 
>> to implement AppenderSelectors and LayoutSelectors.  You probably would want 
>> to dynamically initialize the Appenders much like the RoutingAppender does. 
>> Maybe it would look like:
>> <Appenders>
>>   <ScriptSelector name=“" default=“”>
>>      <Script language=“groovy”><![CDATA[
>>          if (System.getProperty”os.name 
>> <http://os.name/>”).contains(“OS/390”)) then {
>>              return “Socket”;
>>          } else {
>>              return “File”;
>>          }           
>>      </Script>
>>      <Appenders>
>>          <SocketAppender name=“Socket” …/>
>>          <FileAppender name=“File” …/>
>>      </Appenders>     
>>   </ScriptSelector>
>> </Appenders>
>> The thing is that this script would run every time the Selector was accessed 
>> while it sounds like you would only want the script to run when the Selector 
>> is initialized. We could do that too but the script would need to be 
>> declared in a property that would only be used when the selector is 
>> initialized. I would want to support being able to do both.
>> ==copy end==
>> This is indeed like the RoutingAppender _except_ that the whole point is to 
>> do the script selection on start up. When you say that you'd want it both 
>> ways, on start up and on each log event; what would the configuration 
>> difference look like?
>> But.. "Appender that uses a Selector to figure out which Appender to 
>> delegate to" ... that is _so_ much like a RoutingAppender as to be 
>> redundant, no?
> The difference is that a AppenderSelector can just implement the Builder or 
> Factory and invoke the script at that time to figure out which Appender to 
> create. It then returns that Appender. So while the AppenderSelector is 
> technically an Appender, it really is just an AppenderBuilder.  The 
> RoutingAppender is a real Appender.
>> What I want is for the script to determine which appender to use (once), and 
>> instantiate that appender (once). There is no need for one appender to 
>> delegate to another appender.
> And that is what I just described.
>> The more general case is for the script to determine which appenders 
>> (plural) to use (once), and instantiate those appenders (plural) (once). 
>> There is no need for one appender to delegate to another appender list. I do 
>> not have a use case for this today, but I do for the one appender case.
> An AppenderSelector could only instantiate a single Appender, not a group. If 
> you wanted multiple appenders dynamically created this way you would using 
> multiple selectors. I’m not sure I see that as a drawback.
>> My goal would be explained to a user like this: "This feature helps you 
>> build your configuration dynamically, all from the configuration file, to 
>> determine which appender(s) to configure. This is different from using a 
>> RoutingAppender which creates a level of indirection and decides what to do 
>> for each log event _at runtime_" Yes, this is a simpler explanation than 
>> also explaining the new role of scripts in the RoutingAppender but you get 
>> the idea.
>> I am open different solutions that meet the goal of building the 
>> configuration dynamically, as if you'd done it in XML explicitly (or JSON) 
>> but does not end up with one appender delegating to another.
>> Thoughts?
>> Gary
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