Java – logback: Two appenders, multiple loggers, different levels

javalogbacklogging

I want to have two log files in my application (Spring Integration), debug.log and main.log. I want to run main.log at an INFO level and debug.log at a DEBUG level. This is doable with filters on the appenders. I want to log different levels to the appenders based on the source. In other words

<logger name="org.springframework" level="ERROR">
    <appender-ref ref="main" />
</logger>
<logger name="org.springframework" level="DEBUG">
    <appender-ref ref="debug" />
</logger>
<logger name="com.myapp" level="INFO">
    <appender-ref ref="main" />
</logger>
<logger name="com.myapp" level="DEBUG">
    <appender-ref ref="debug" />
</logger>

So to summarise:

  1. Spring logger
    • main -> ERROR
    • debug -> DEBUG
  2. com.myapp logger
    • main -> INFO
    • debug -> DEBUG

Because of this I have to have the loggers running at DEBUG and a threshold filter on an appender isn't fine grained enough.

Update Added clarity to the question

Best Answer

Create a ThresholdLoggerFilter class which can be put on an appender like:

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
        <level>INFO</level>
    </filter>
    <filter class="com.myapp.ThresholdLoggerFilter">
        <logger>org.springframework</logger>
        <level>ERROR</level>
    </filter>
    </appender>

The following code works

package com.myapp;

import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.filter.Filter;
import ch.qos.logback.core.spi.FilterReply;

public class ThresholdLoggerFilter extends Filter<ILoggingEvent> {
    private Level level;
    private String logger;

    @Override
    public FilterReply decide(ILoggingEvent event) {
        if (!isStarted()) {
            return FilterReply.NEUTRAL;
        }

        if (!event.getLoggerName().startsWith(logger))
            return FilterReply.NEUTRAL;

        if (event.getLevel().isGreaterOrEqual(level)) {
            return FilterReply.NEUTRAL;
        } else {
            return FilterReply.DENY;
        }
    }

    public void setLevel(Level level) {
        this.level = level;
    }

    public void setLogger(String logger) {
        this.logger = logger;
    }

    public void start() {
        if (this.level != null && this.logger != null) {
            super.start();
        }
    }
}
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