log4j.properties File Example [Latest]

Since properties file don’t have any defined schema to validate, we have to be more careful with it. Today we will see how XML configurations can be converted to properties based configuration.

Root Logger

Root logger is used when there is no match with a logger. It’s defined like below in XML.

<root>
	<priority value="DEBUG" />
	<appender-ref ref="file" />
	<appender-ref ref="console" />
</root>

It can be defined in properties file as below.

log4j.rootLogger=DEBUG, file, console

The first value in comma separated list is the root logging level value. All other values are appenders.

Log4j Appenders

We can have multiple appenders in log4j. Below are two appenders, one for console logging and another to file.

<!-- console appender -->
<appender name="console" class="org.apache.log4j.ConsoleAppender">
	<param name="Target" value="System.out" />
	<layout class="org.apache.log4j.PatternLayout">
		<param name="ConversionPattern" value="%-5p %c{1} - %m%n" />
	</layout>
</appender>
<!-- rolling file appender -->
<appender name="file" class="org.apache.log4j.RollingFileAppender">
	<param name="File" value="logs/main.log" />
	<param name="Append" value="true" />
	<param name="ImmediateFlush" value="true" />
	<param name="MaxFileSize" value="10MB" />
	<param name="MaxBackupIndex" value="5" />
	<layout class="org.apache.log4j.PatternLayout">
		<param name="ConversionPattern" value="%d %d{Z} [%t] %-5p (%F:%L) - %m%n" />
	</layout>
</appender>

In log4j.properties file, they will be defined as below.

#Define console appender
log4j.appender.console=org.apache.log4j.ConsoleAppender
logrj.appender.console.Target=System.out
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-5p %c{1} - %m%n
#Define rolling file appender
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=logs/main.log
log4j.appender.file.Append=true
log4j.appender.file.ImmediateFlush=true
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=5
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d %d{Z} [%t] %-5p (%F:%L) - %m%n

So the format for log4j properties file appender is log4j.appender.{appender_name}.{appender_config}. Notice that the appenders configurations such as MaxFileSize, MaxBackupIndex are same as in XML configuration file.

Log4j loggers

Just like appenders, we can have multiple loggers. For example of xml based configuration;

<logger name="com.journaldev.log4j" additivity="false">
	<level value="WARN" />
	<appender-ref ref="file" />
	<appender-ref ref="console" />
</logger>
<logger name="com.journaldev.log4j.logic" additivity="false">
	<level value="DEBUG" />
	<appender-ref ref="file" />
</logger>

They will be defined in properties file as log4j.logger.{logger_name}. The values contain logging level and list of appenders to use.

#Define loggers
log4j.logger.com.journaldev.log4j=WARN, file, console
log4j.logger.com.journaldev.log4j.logic=DEBUG, file, console

Log4j logger additivity

Additivity usage is shown in above logger xml configuration, it’s the attribute of logger element. Below is the way to use it in log4j properties file configuration as log4j.additivity.{logger_name}.

#setting additivity
log4j.additivity.com.journaldev.log4j=false
log4j.additivity.com.journaldev.log4j.logic=false

Based on above, below is my final log4j.properties file.

#Define root logger options
log4j.rootLogger=DEBUG, file, console
#Define console appender
log4j.appender.console=org.apache.log4j.ConsoleAppender
logrj.appender.console.Target=System.out
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-5p %c{1} - %m%n
#Define rolling file appender
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=logs/main.log
log4j.appender.file.Append=true
log4j.appender.file.ImmediateFlush=true
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=5
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d %d{Z} [%t] %-5p (%F:%L) - %m%n
#Define loggers
log4j.logger.com.journaldev.log4j=WARN, file, console
log4j.logger.com.journaldev.log4j.logic=DEBUG, file, console
#setting additivity
log4j.additivity.com.journaldev.log4j=false
log4j.additivity.com.journaldev.log4j.logic=false

Log4j PropertyConfigurator

PropertyConfigurator is used to configure log4j settings. It’s optional if the file name is log4j.properties and it’s in the project classpath. We have to configure it before using the logger.

Here is a simple program showing how to configure and use log4j logging.

package com.journaldev.log4j.main;
import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;
import com.journaldev.log4j.logic.MathUtils;
public class Log4jExample {
	static{
		init();
	}
	private final static Logger logger = Logger.getLogger(Log4jExample.class);
	public static void main(String[] args) {
		logger.debug("My Debug Log");
		logger.info("My Info Log");
		logger.warn("My Warn Log");
		logger.error("My error log");
		logger.fatal("My fatal log");
	}
	/**
	 * method to init log4j configurations
	 */
	private static void init() {
		PropertyConfigurator.configure("log4j.properties");
	}
}

When it’s executed, you will get below in console log.

WARN  Log4jExample - My Warn Log
ERROR Log4jExample - My error log
FATAL Log4jExample - My fatal log

At the same time, you will see logs getting generated in main.log file as below.

2016-05-14 00:34:11,994 +0530 [main] WARN  (Log4jExample.java:20) - My Warn Log
2016-05-14 00:34:11,995 +0530 [main] ERROR (Log4jExample.java:21) - My error log
2016-05-14 00:34:11,995 +0530 [main] FATAL (Log4jExample.java:22) - My fatal log

Notice that debug and info logger are not getting printed because the minimum logging level is set as WARN. That’s all for log4j properties file example usage. Happy Logging!