Re: OS-based dynamic configuration file

Gary Gregory Sun, 18 Sep 2016 21:44:25 -0700

Hm, but how? org.apache.logging.log4j.core.appender.AbstractAppender.name
is final and there is no Appender.setName(String). Surely, we should not
use reflection...


Gary

On Sun, Sep 18, 2016 at 9:34 PM, Ralph Goers <ralph.go...@dslextreme.com>
wrote:

> 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.
>
> Ralph
>
> 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>
> wrote:
>
>> See inline
>>
>> On Sep 16, 2016, at 10:31 PM, Gary Gregory <garydgreg...@gmail.com>
>> wrote:
>>
>> On Fri, Sep 16, 2016 at 8:38 PM, Ralph Goers <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”).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
>>
>>
>
>
> --
> E-Mail: garydgreg...@gmail.com | ggreg...@apache.org
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>
>
>


-- 
E-Mail: garydgreg...@gmail.com | ggreg...@apache.org
Java Persistence with Hibernate, Second Edition
<http://www.manning.com/bauer3/>
JUnit in Action, Second Edition <http://www.manning.com/tahchiev/>
Spring Batch in Action <http://www.manning.com/templier/>
Blog: http://garygregory.wordpress.com
Home: http://garygregory.com/
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Re: OS-based dynamic configuration file

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