Initializing Log4j

Document  Version 1.0

Copyright © 2012-2013 beijing.beijing.012@gmail.com

You might have ever seen following warning running your program:

log4j:WARN No appenders could be found for logger (MyLogger).
log4j:WARN Please initialize the log4j system properly.

What does this mean?

It means Log4j is not initialized for your application.

Log4j could be initialized by using Log4j configurators. A more convenient way however is to provide a Log4j configuration file as JVM parameter, and let Log4j do the initialization. I will show you how does this work with a small program  now:


Sample code:

package tryl4j;

import org.apache.log4j.Logger;

/**
 * @author swang
 *
 */
public class TryLog4jInit {
private static final Logger logger = Logger.getLogger("MyLogger");
public static void main(String[] ages) {
logger.info("Did you add  a  JVM param for initializing log4j?");
}

}

log4j.properties  file

# Root logger option
log4j.rootLogger=INFO, stdout

# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

Run the above class with:

 -Dlog4j.configuration="file:/tmp/log4j.properties"

And you will see the warning is not showing up and more, and you  see the logged info in console:

2013-06-23 12:13:17 INFO  MyLogger:16 - Did you add  a  JVM param for  initializing log4j?

So the JVM parameter works!