Basic Log4j PatternLayout with elapsed time extension using joda time

TimeElapsedPatternLayout.java

package com.stackoverflow;

import org.apache.log4j.PatternLayout;
import org.apache.log4j.spi.LoggingEvent;
import org.joda.time.Period;
import org.joda.time.format.PeriodFormatter;
import org.joda.time.format.PeriodFormatterBuilder;
import java.lang.management.ManagementFactory;

/**
 * Shows how to extend PatternLayout to write your ouwn log entries.
 * in this case it presfixes all lines with a human readable elapsed time prefix.
 * looks like this:
 * 0:00:15.904 - DEBUG [main] a test
 */
public class TimeElapsedPatternLayout extends PatternLayout {
	PeriodFormatter formatter = new PeriodFormatterBuilder()
			.printZeroIfSupported()
			.appendHours()
			.appendSeparator(":")
			.minimumPrintedDigits(2)
			.appendMinutes()
			.appendSeparator(":")
			.appendSecondsWithMillis()
			.appendLiteral(" - ")
			.toFormatter();
	
	@Override
	public String format(LoggingEvent event) {
    //using upTime to be independent of the time this class get loaded
		String prefix = formatter.print(new Period(ManagementFactory.getRuntimeMXBean().getUptime()));
		return prefix + super.format(event);
	}
}