Log4j 2 XML Configuration Example

Apache Log4j 2 is an upgrade to Log4j 1.x that provides significant improvements over its predecessor such as performance improvement, automatic reloading of modified configuration files, java 8 lambda support and custom log levels.

To include Log4j2 in your project, include below dependency in your project.

<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-api</artifactId>
	<version>2.6.1</version>
</dependency>
<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-core</artifactId>
	<version>2.6.1</version>
</dependency>

log4j2.xml for logging into Console

You can use below log4j2.xml file logging output into console. Please note that if no configuration file could be located then DefaultConfiguration will be used. This also causes logging output to go to the console.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
	<Appenders>
		<Console name="console" target="SYSTEM_OUT">
			<PatternLayout
				pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
		</Console>
	</Appenders>
	<Loggers>
		<Root level="debug" additivity="false">
			<AppenderRef ref="console" />
		</Root>
	</Loggers>
</Configuration>

log4j2.xml for logging into rolling files

You can use below log4j2.xml file logging output into date based rolling files – along with console.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn">
	<Properties>
		<Property name="basePath">C:\\logs</Property>
	</Properties>

	<Appenders>
		<RollingFile name="fileLogger" fileName="${basePath}/app-info.log" filePattern="${basePath}/app-info-%d{yyyy-MM-dd}.log">
			<PatternLayout>
				<pattern>[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n</pattern>
			</PatternLayout>
			<Policies>
				<TimeBasedTriggeringPolicy interval="1" modulate="true" />
			</Policies>
		</RollingFile>

		<Console name="console" target="SYSTEM_OUT">
			<PatternLayout	pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
		</Console>
	</Appenders>
	<Loggers>
		<Logger name="com.howtodoinjava" level="debug" additivity="true">
			<appender-ref ref="fileLogger" level="debug" />
		</Logger>
		<Root level="debug" additivity="false">
			<appender-ref ref="console" />
		</Root>
	</Loggers>
</Configuration>

log4j2.xml file location

You should put log4j2.xml anywhere in application’s classpath. Log4j will scan all classpath locations to find out this file and then load it.

log4j2.xml example

Let’s write a java class and write few log statements to verify that logs are appreaing in console and log file as well.

package com.howtodoinjava.log4j2.examples;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Log4j2HelloWorldExample 
{
	private static final Logger LOGGER = LogManager.getLogger(Log4j2HelloWorldExample.class.getName());
	
	public static void main(String[] args) 
	{
		LOGGER.debug("Debug Message Logged !!!");
		LOGGER.info("Info Message Logged !!!");
		LOGGER.error("Error Message Logged !!!", new NullPointerException("NullError"));
	}
}

Now when you run the above program, you will get below logs in console.

[DEBUG] 2016-06-16 12:17:42.972 [main] Log4j2HelloWorldExample - Debug Message Logged !!!
[INFO ] 2016-06-16 12:17:42.996 [main] Log4j2HelloWorldExample - Info Message Logged !!!
[ERROR] 2016-06-16 12:17:42.997 [main] Log4j2HelloWorldExample - Error Message Logged !!!
java.lang.NullPointerException: NullError
	at com.howtodoinjava.log4j2.examples.Log4j2HelloWorldExample.main(Log4j2HelloWorldExample.java:14) [classes/:?]

If you change the system date and run the application again, you will find two log files in configured location i.e. app-info.log and app-info-2016-06-15.log – where second file is rolled over file.

Happy Learning !!