How can I configure Logback to log different levels for a logger to different destinations?

Question

How can I configure Logback to log different levels for a logger to different destinations?

For example, given the following Logback configuration, will Logback reco

Answer 1

I take no credit for this answer, as it's merely a combination of the best two answers above: that of X. Wo Satuk and that of Sébastien Helbert: ThresholdFilter is lovely but you can't configure it to have an upper level as well as a lower level*, but combining it with two LevelFilters set to "DENY" WARN and ERROR works a treat.

Very important: do not forget the System.err tag in the STDERR appender: my omission of it had me frustrated for a few minutes.

    
    
        
            INFO
        
        
            WARN
            DENY
        
        
            ERROR
            DENY
        
        
            %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36}.%M\(%line\)
                - %msg%n
            
        
    

    
        
            WARN
        
        System.err
        
            %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36}.%M\(%line\)
                - %msg%n
            
        
    

    
        
        
    

* it does however have a method decide in the API but I haven't a clue how you'd use it in this context.