[logback-user] How to send one event to more than one appender using the SiftingAppender?

Konstantinidis, Johannes johannes.konstantinidis at capgemini.com
Fri Apr 19 17:40:40 CEST 2013

Hi David,

thanks for the answer.

I thought about subclassing the Sifting Appender because the SiftingAppender and its configuration offer nearly everything I need. If I add a new appender, it would at least need the name of the SiftingAppender. So I would need an Action and a description how to configure, while the SiftingAppender configuration is standard and has been described already.

In addition, as mentioned before in another conversation on this list, the SiftingAppender creates a sub appender only if there is at least one message for the sub appender. So wouldn't I run into the same problem to just send a dummy message to create the appender. Otherwise the valueList would not contain the appender, would it?

Btw, I have a working "subclass" of SiftingAppender that does the job. Because of the package-private code in SiftingAppenderBase it is more like a copy than a subclass :-) It would be helpful to split the SiftingAppenderBase's append(..) method into two parts:
- get discriminating value
- get appender and doAppend
So a subclass can use the first method to get the discriminating value and manipulate it and the second method to append to one or more appenders.


-----Ursprüngliche Nachricht-----
Von: Logback-user [mailto:logback-user-bounces at qos.ch] Im Auftrag von diroussel
Gesendet: Freitag, 19. April 2013 15:10
An: logback-user at qos.ch
Betreff: Re: [logback-user] How to send one event to more than one appender using the SiftingAppender?


I can't see how that would work at the moment.

SiftingAppender keeps it's child appenders, and when a log events comes in
it will only log to one of them.

I suppose, if you can write a custom appender that gets a reference to the
SiftingAppender, then you can do this:

class FanOutAppender implements Appender {
  SiftingAppender sift;
  void doAppend(E event) {
    // Fan out log event to all child appenders of sift
    for (Appender a : sift.getAppenderTracker().valueList()) {

And that will log to all appenders.  The trick is using filters so your log
event goes to either the sifting appender or your custom FanOutAppender


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