[logback-user] Multiple layouts for a single appender

ceki ceki at qos.ch
Thu May 24 12:17:02 CEST 2012

On 16.05.2012 15:27, Y M wrote:

 > Hello,

 > My situation is this: on certain specific and frequent log
 > statements, I need the stacktrace to identify the method that needs to
 > be investigated. However, the whole stacktrace is too long and
 > unnecessary in this case (it is generating too much logging and
 > garbage), but in every other, it is useful. I'd like to change the
 > layout for this situation, and use %throwable{5}, for example.
 > So, I found nothing on the manual similar to this, and nothing
 > searching around, maybe I'll need a custom class. If so, how could I
 > do it? Multiple filtered appenders writing to the same file seems too
 > much overhead and troublesome- I think the best approach would be a
 > custom encoder, and do the selection inside 'doEncode', based on some
 > event parameter, probably a specific marker. I'm just analyzing the
 > possibilities, no coding yet, so I'm not aware of any shortcomings or
 > limitations.

There is support exactly for this type of situation. See the docs for
PatternLayout [1]. In particular, the docs on %ex conversion
word. Here is the relevant quote:

This conversion word can also use evaluators to test logging events
against a given criterion before creating the output. For example,
using %ex{full, EX_DISPLAY_EVAL} will display the full stack trace of
the exception only if the evaluator called EX_DISPLAY_EVAL returns a
negative answer. Evaluators are described further down in this

Refer to [2] for evaluators.

Let us know if this approach works for you.

[1] http://logback.qos.ch/manual/layouts.html#ClassicPatternLayout
[2] http://logback.qos.ch/manual/layouts.html#Evaluators


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