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From "Bruce Brouwer (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LOG4J2-585) Markers not as powerful as slf4j
Date Sun, 30 Mar 2014 13:06:14 GMT
Bruce Brouwer created LOG4J2-585:
------------------------------------

             Summary: Markers not as powerful as slf4j
                 Key: LOG4J2-585
                 URL: https://issues.apache.org/jira/browse/LOG4J2-585
             Project: Log4j 2
          Issue Type: Improvement
          Components: API
    Affects Versions: 2.0-rc1
            Reporter: Bruce Brouwer


Log4J's markers are not as flexible as markers in SLF4J. 

First, SLF4J's markers are mutable. By allowing markers to be mutable, I can change the relationship
of markers to each other based upon runtime or business conditions. 

Second, and more importantly I think, is that essentially SLF4J markers have this parent/child
relationship, much like Log4J, except that in SLF4J, I can essentially have a marker with
multiple parents. For example, I might want this structure:
* Animal
** Bird
*** Duck
** Mammal
*** Bear
*** Dolphin
* Travels by
** Water
*** Duck
*** Dolphin
** Land
*** Duck
*** Bear
** Air
*** Duck

Of course, this is a contrived example, but I wanted to describe the relationships. Now, if
I wanted to filter based on markers that travel by Water for some appenders, and another appender
wants to filter by Mammals, I can't simply use the single marker of Dolphin. 

Either we need to reverse the marker relationship so that it contains its children, much like
SLF4J, or we allow markers to have multiple parents, which I prefer because it could make
it more succinct to define:
{code}
private static final Marker BY_LAND = MarkerManager.getMarker("BY_LAND");
private static final Marker BY_WATER = MarkerManager.getMarker("BY_WATER");
private static final Marker DUCK = MarkerManager.getMarker("DUCK", BY_LAND, BY_WATER);
{code}

As for the Marker API, we would either need to change getParent to getParents, or get rid
of the getParent method from the API and just rely on the isInstanceOf method to handle checking
multiple parents by looking at private member variables (my preference)



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