by Janice Carriger at Pexels

Colored logs with Logback

This will color-code your log levels in the console output, which helps to quickly identify errors and warnings as you scroll.

The overall approach is:

• Add a class that extends Logback’s ForegroundCompositeConverterBase<ILoggingEvent> and handles color determination logic
• Add a <conversionRule> in your Logback XML configuration with a conversionWord to identify it
• Incorporate the conversion rule into your log pattern via the conversionWord

Here’s my Converter implementation:

package me.alexandercalvert.logback;

import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.spi.ILoggingEvent;
import static ch.qos.logback.core.pattern.color.ANSIConstants.*;
import ch.qos.logback.core.pattern.color.ForegroundCompositeConverterBase;

public class HighlightingConverter extends ForegroundCompositeConverterBase<ILoggingEvent> {

	@Override
	protected String getForegroundColorCode(ILoggingEvent event) {
		Level level = event.getLevel();
		switch (level.toInt()) {
		case Level.ERROR_INT:
			return BOLD + RED_FG;
		case Level.WARN_INT:
			return YELLOW_FG;
		case Level.INFO_INT:
			return GREEN_FG;
		default:
			return DEFAULT_FG;
		}
	}

}

and my logback.xml. Notice that the converterClass attribute on the <conversionRule> tag is the fully qualified name of the Converter implementation:

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true">

    <conversionRule conversionWord="customhighlight" converterClass="me.alexandercalvert.logback.HighlightingConverter"/>

    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{ISO8601} %cyan([%thread]) %customhighlight(%-5level) %cyan(%logger{36}) - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="info">
        <appender-ref ref="STDOUT"/>
    </root>

</configuration>