uguy / log4j2-simple

Basic playground to play with log4j2

Log4j2 Playground

Exploration of some composite configuration capabilities of log4j2.

Build

This a simple maven project (with wrapper as an option) using java 17

Just perform ./mvnw package (or ./mvnw clean package if you want to get rid of previous log files). This will produce a executable fat jar in the target/ folder.

Configuration

The App support some pre-configured appenders out the box (see Startup) but additional configuration can be used. If you choose to do so, you should add the base configuration file (classpath:log4j2/base.xml) to the list and then your custom ones by using the jvm property log4j2.configurationFile

java -Dlog4j2.configurationFile="classpath:log4j2/base.xml,file:log4j2-config.xml" -Dlogger.appenders="CONSOLE_PLAIN" -jar target/log4jsimple-1.0.0-SNAPSHOT.jar

log4j2-config.xml could be an externalized file to be used by the App OPS for more customization.

This file can contain any extra log4j2 configuration like more appenders, etc.

Sample log4j2-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration monitorInterval="30">
<!--	<Appenders>-->
<!--		<File name="MyFile" fileName="target/my_app.log">-->
<!--			<PatternLayout>-->
<!--				<Pattern>%d %p %c{1.} [%t] %m%n</Pattern>-->
<!--			</PatternLayout>-->
<!--		</File>-->
<!--	</Appenders>-->
	<Loggers>
		<Root level="INFO">
<!--			<AppenderRef ref="MyFile"/>-->
		</Root>
		<Logger name="org.example.internal" level="DEBUG"/>
	</Loggers>
</Configuration>

Startup

App can be started using jvm property logger.appenders to enable preconfigured appenders like CONSOLE_PLAIN, CONSOLE_JSON, CONSOLE_ECS, FILE, …​ )

#Push logs to file only
java -Dlogger.appenders="FILE" -jar target/log4jsimple-1.0.0-SNAPSHOT.jar

#Push logs to console as plain text and file
java -Dlogger.appenders="CONSOLE_PLAIN,FILE" -jar target/log4jsimple-1.0.0-SNAPSHOT.jar

Sample output for CONSOLE_ECS

{"@timestamp":"2023-05-26T13:00:20.467Z","log.level":"DEBUG","message":"debug msg", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.App","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.469Z","log.level": "INFO","message":"info msg", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.App","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.469Z","log.level": "WARN","message":"warn msg", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.App","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.469Z","log.level":"DEBUG","message":"debug work", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.internal.MyComponent","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.469Z","log.level": "INFO","message":"info work", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.internal.MyComponent","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.469Z","log.level": "WARN","message":"warn work", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.internal.MyComponent","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287"}
{"@timestamp":"2023-05-26T13:00:20.470Z","log.level":"ERROR","message":"An work error occurred", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.internal.MyComponent","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287","error.type":"java.lang.RuntimeException","error.message":"Oops work exception !","error.stack_trace":"java.lang.RuntimeException: Oops work exception !\n\tat org.example.internal.MyComponent.work(MyComponent.java:13)\n\tat org.example.App.main(App.java:17)\n"}
{"@timestamp":"2023-05-26T13:00:20.470Z","log.level":"ERROR","message":"An error occurred", "ecs.version": "1.2.0","process.thread.name":"main","log.logger":"org.example.App","service.name":"log4jsimple","service.version":"1.0.0-SNAPSHOT","service.node.name":"LAP-00287","error.type":"java.lang.RuntimeException","error.message":"Oops exception !","error.stack_trace":"java.lang.RuntimeException: Oops exception !\n\tat org.example.App.main(App.java:19)\n"}

Notes

• XIncludes cannot be used to mix configurations from inside the classpath and outside the classpath.

• Using a system property for the appender name itself is a bad idea because is evaluated on each log event (instead of once at startup for ScriptAppenderSelector)

• Elastic Common Schema (ECS) : https://www.elastic.co/fr/what-is/ecs